共用题干第三篇Only special plants can survive in the terrible climate of a desert,for these are regions where the annual range of the soil temperature can be over 75℃.Furthermore,during the summer there are few clouds in the sky to protect plants from the sun's ray.Another problem is the fact that there are frequently strong winds which drive small-sharp particles of sand into the plants,tearing and damaging them.The most difficult problem for all forms of plant life,however,is the fact that the entire annual rainfall occurs during a few days or weeks in spring.Grasses and flowers in desert survive from one year to the next by existing through the long, hot,dry season in the form of seeds.These seeds remain inactive unless the right amount of rain falls.If no rain falls,or if insufficient rain falls,they wait until the next year,or even still the next.Another factor that helps these plants to survive is the fact that their life cycles are short.By the time that the water from the spring rains disappears—ust a few weeks after it falls一such plants no longer need any.The perennials（多年生植物）have special features which enable them to survive as plants for several years. Thus,nearly all desert perennials have extensive root systems below ground and a small shoot system above ground.The large root network enables the plant to absorb as much water as possible in a short time.The small shoot system,on the other hand,considerably limits water loss by evaporation（蒸发）.Another feature of many desert perennials is that after the rainy season they lose their leaves in preparation for the long,dry season,just as trees in wetter climates lose theirs in preparation for the winter. This reduces their water loss by evaporation during the dry season.Then,in the next rainy season,they come fully alive once more,and grow new branches,leaves and flowers,just as the grasses and flowers in desert do.The last paragraph is mainly about__________.A:the comparison between plants in different areasB:the growth of new leaves in the rainy seasonC:water loss by evaporation in the dry seasonD:the changes in the leaves of the perennials
共用题干
第三篇
Only special plants can survive in the terrible climate of a desert,for these are regions where the annual range of the soil temperature can be over 75℃.Furthermore,during the summer there are few clouds in the sky to protect plants from the sun's ray.Another problem is the fact that there are frequently strong winds which drive small-sharp particles of sand into the plants,tearing and damaging them.The most difficult problem for all forms of plant life,however,is the fact that the entire annual rainfall occurs during a few days or weeks in spring.
Grasses and flowers in desert survive from one year to the next by existing through the long, hot,dry season in the form of seeds.These seeds remain inactive unless the right amount of rain falls.If no rain falls,or if insufficient rain falls,they wait until the next year,or even still the next.
Another factor that helps these plants to survive is the fact that their life cycles are short.By the time that the water from the spring rains disappears—ust a few weeks after it falls一such plants no longer need any.
The perennials（多年生植物）have special features which enable them to survive as plants for several years. Thus,nearly all desert perennials have extensive root systems below ground and a small shoot system above ground.The large root network enables the plant to absorb as much water as possible in a short time.The small shoot system,on the other hand,considerably limits water loss by evaporation（蒸发）.
Another feature of many desert perennials is that after the rainy season they lose their leaves in preparation for the long,dry season,just as trees in wetter climates lose theirs in preparation for the winter. This reduces their water loss by evaporation during the dry season.Then,in the next rainy season,they come fully alive once more,and grow new branches,leaves and flowers,just as the grasses and flowers in desert do.
第三篇
Only special plants can survive in the terrible climate of a desert,for these are regions where the annual range of the soil temperature can be over 75℃.Furthermore,during the summer there are few clouds in the sky to protect plants from the sun's ray.Another problem is the fact that there are frequently strong winds which drive small-sharp particles of sand into the plants,tearing and damaging them.The most difficult problem for all forms of plant life,however,is the fact that the entire annual rainfall occurs during a few days or weeks in spring.
Grasses and flowers in desert survive from one year to the next by existing through the long, hot,dry season in the form of seeds.These seeds remain inactive unless the right amount of rain falls.If no rain falls,or if insufficient rain falls,they wait until the next year,or even still the next.
Another factor that helps these plants to survive is the fact that their life cycles are short.By the time that the water from the spring rains disappears—ust a few weeks after it falls一such plants no longer need any.
The perennials（多年生植物）have special features which enable them to survive as plants for several years. Thus,nearly all desert perennials have extensive root systems below ground and a small shoot system above ground.The large root network enables the plant to absorb as much water as possible in a short time.The small shoot system,on the other hand,considerably limits water loss by evaporation（蒸发）.
Another feature of many desert perennials is that after the rainy season they lose their leaves in preparation for the long,dry season,just as trees in wetter climates lose theirs in preparation for the winter. This reduces their water loss by evaporation during the dry season.Then,in the next rainy season,they come fully alive once more,and grow new branches,leaves and flowers,just as the grasses and flowers in desert do.
The last paragraph is mainly about__________.
A:the comparison between plants in different areas
B:the growth of new leaves in the rainy season
C:water loss by evaporation in the dry season
D:the changes in the leaves of the perennials
A:the comparison between plants in different areas
B:the growth of new leaves in the rainy season
C:water loss by evaporation in the dry season
D:the changes in the leaves of the perennials
参考解析
解析：细节题。第一段前三句分别列举了影响植物在沙漠中生长的三个因素： soil temperature（选项D) ,sun's rays（选项B ) , strong winds（选项A)。只有选项C没有提及。
推理判断题。可根据第二段前三句推断出答案。选项A无原文依据，选项B前半句不对，选项D则有悖常理。
细节题。本题解题的关键是注意题干是关于shoot system的提问，而不是 root system。在第三段最后一句可找到相关信息，并由此可确定选项D为正确选项。
推理判断题：第一段的最后一句谈到降雨量集中在春天，第二段第二句谈到种子在下雨季节才发芽生长，由此可推断出选项B正确。其余三项均无原文依据。
主旨大意题。第四段第一句通过Another feature引出本段的主题句，本句的中心词是perennials和leaves，据此可以判断选项D正确。其他选项均没有关注这两个中心词。
推理判断题。可根据第二段前三句推断出答案。选项A无原文依据，选项B前半句不对，选项D则有悖常理。
细节题。本题解题的关键是注意题干是关于shoot system的提问，而不是 root system。在第三段最后一句可找到相关信息，并由此可确定选项D为正确选项。
推理判断题：第一段的最后一句谈到降雨量集中在春天，第二段第二句谈到种子在下雨季节才发芽生长，由此可推断出选项B正确。其余三项均无原文依据。
主旨大意题。第四段第一句通过Another feature引出本段的主题句，本句的中心词是perennials和leaves，据此可以判断选项D正确。其他选项均没有关注这两个中心词。
相关考题：
EA rainforest is an area covered by tall trees with the total high rainfall spreading quite equally through the year and the temperature rarely dipping below l6℃．Rainforests have a great effect on the world environment because they can take in heat from the sun and adjust the climate．Without the forest cover，these areas would reflect more heat into the atmosphere，warming the rest of the world. Losing the rainforests may also influence wind and rainfall patterns，potentially causing certain natural disasters all over the world．In the past hundred years，humans have begun destroying rainforests in search of three major resources(资源)：land for crops，wood for paper and other products，land for raising farm animals．This action affects the environment as a whole．For example，a lot of carbon dioxide (二氧化碳)in the air comes from burning the rainforests．People obviously have a need for the resources we gain from cutting trees but we will suffer much more than we will benefit.There are two main reasons for this．Firstly，when people cut down trees，generally they can only use the land for a year or two．Secondly，cutting large sections of rainforests may provide a good supply of wood right now，but in the long run it actually reduces the world’s wood supply．Rainforests are often called the world’s drug store．More than 25％ of the medicines we use today come from plants in rainforests．However，fewer than l％of rainforest plants have been examined for their medical value．It is extremely likely that our best chance to cure diseases lies somewhere in the world’s shrinking rainforests．72．Rainforests can help to adjust the climate because they ．A．reflect more heat into the atmosphereB．bring about high rainfall throughout the worldC．rarely cause the temperature to drop lower than l6℃D．reduce the effect of heat from the sun on the earth
AWhy do plants grow in some places and not in others? Why does some land have so much growing on it，while other land has almost no plants growing on it at all?To grow plants need several things． One is warmth． In very cold places almost nothing grows． Plants also need water． In very dry parts of the earth only a few unusual plants can grow． That's why dry deserts everywhere are almost not covered by trees or grass．Plants must also have a place in which to f，ut down their roots and grow． They find it diffi-culr to grow on hard land． The town is built on hard land． The plants here have only the soil found between the cracks of the stones Io grow in．Another thing plants must have before they can grow is food．Whar will happen if we try to make things grow on the sandy beach? A few plants，such as beach grass，will grow in sand，L ut most plants won-t． Even if the weather is warm enough．and we water the plants each day． Many of them will die because the sand on this beach has al-most no food for plants．( )21． According to the passage，plants need _________ things to grow well．A． twoB． threeC． fourD． five
共用题干第三篇Only special plants can survive in the terrible climate of a desert,for these are regions where the annual range of the soil temperature can be over 75℃.Furthermore,during the summer there are few clouds in the sky to protect plants from the sun's ray.Another problem is the fact that there are frequently strong winds which drive small-sharp particles of sand into the plants,tearing and damaging them.The most difficult problem for all forms of plant life,however,is the fact that the entire annual rainfall occurs during a few days or weeks in spring.Grasses and flowers in desert survive from one year to the next by existing through the long, hot,dry season in the form of seeds.These seeds remain inactive unless the right amount of rain falls.If no rain falls,or if insufficient rain falls,they wait until the next year,or even still the next.Another factor that helps these plants to survive is the fact that their life cycles are short.By the time that the water from the spring rains disappears—ust a few weeks after it falls一such plants no longer need any.The perennials（多年生植物）have special features which enable them to survive as plants for several years. Thus,nearly all desert perennials have extensive root systems below ground and a small shoot system above ground.The large root network enables the plant to absorb as much water as possible in a short time.The small shoot system,on the other hand,considerably limits water loss by evaporation（蒸发）.Another feature of many desert perennials is that after the rainy season they lose their leaves in preparation for the long,dry season,just as trees in wetter climates lose theirs in preparation for the winter. This reduces their water loss by evaporation during the dry season.Then,in the next rainy season,they come fully alive once more,and grow new branches,leaves and flowers,just as the grasses and flowers in desert do.We can learn from the passage that the shoot system of the perennials_________.A:can help the perennials absorb less of the sun's rayB:decides the appearance of the perennials in desertC:limits the function of the perennials' branchesD:may prevent the perennials from losing much water
共用题干第三篇Only special plants can survive in the terrible climate of a desert,for these are regions where the annual range of the soil temperature can be over 75℃.Furthermore,during the summer there are few clouds in the sky to protect plants from the sun's ray.Another problem is the fact that there are frequently strong winds which drive small-sharp particles of sand into the plants,tearing and damaging them.The most difficult problem for all forms of plant life,however,is the fact that the entire annual rainfall occurs during a few days or weeks in spring.Grasses and flowers in desert survive from one year to the next by existing through the long, hot,dry season in the form of seeds.These seeds remain inactive unless the right amount of rain falls.If no rain falls,or if insufficient rain falls,they wait until the next year,or even still the next.Another factor that helps these plants to survive is the fact that their life cycles are short.By the time that the water from the spring rains disappears—ust a few weeks after it falls一such plants no longer need any.The perennials（多年生植物）have special features which enable them to survive as plants for several years. Thus,nearly all desert perennials have extensive root systems below ground and a small shoot system above ground.The large root network enables the plant to absorb as much water as possible in a short time.The small shoot system,on the other hand,considerably limits water loss by evaporation（蒸发）.Another feature of many desert perennials is that after the rainy season they lose their leaves in preparation for the long,dry season,just as trees in wetter climates lose theirs in preparation for the winter. This reduces their water loss by evaporation during the dry season.Then,in the next rainy season,they come fully alive once more,and grow new branches,leaves and flowers,just as the grasses and flowers in desert do.According to the passage,spring is the best time for plants in desert_________.A:to find a shady placeB:to get water for their growthC:to reduce water lossD:to enjoy the sunshine
共用题干第三篇Only special plants can survive in the terrible climate of a desert,for these are regions where the annual range of the soil temperature can be over 75℃.Furthermore,during the summer there are few clouds in the sky to protect plants from the sun's ray.Another problem is the fact that there are frequently strong winds which drive small-sharp particles of sand into the plants,tearing and damaging them.The most difficult problem for all forms of plant life,however,is the fact that the entire annual rainfall occurs during a few days or weeks in spring.Grasses and flowers in desert survive from one year to the next by existing through the long, hot,dry season in the form of seeds.These seeds remain inactive unless the right amount of rain falls.If no rain falls,or if insufficient rain falls,they wait until the next year,or even still the next.Another factor that helps these plants to survive is the fact that their life cycles are short.By the time that the water from the spring rains disappears—ust a few weeks after it falls一such plants no longer need any.The perennials（多年生植物）have special features which enable them to survive as plants for several years. Thus,nearly all desert perennials have extensive root systems below ground and a small shoot system above ground.The large root network enables the plant to absorb as much water as possible in a short time.The small shoot system,on the other hand,considerably limits water loss by evaporation（蒸发）.Another feature of many desert perennials is that after the rainy season they lose their leaves in preparation for the long,dry season,just as trees in wetter climates lose theirs in preparation for the winter. This reduces their water loss by evaporation during the dry season.Then,in the next rainy season,they come fully alive once more,and grow new branches,leaves and flowers,just as the grasses and flowers in desert do.Some grasses and flowers can survive in the desert because__________.A:they need little water for their survivalB:they bear long roots and the seeds are fit for dry weatherC:they stay in the form of seeds to wait for the right armiount of waterD:with long roots,they do not depend on the rain to get enough water
共用题干第三篇Only special plants can survive in the terrible climate of a desert,for these are regions where the annual range of the soil temperature can be over 75℃.Furthermore,during the summer there are few clouds in the sky to protect plants from the sun's ray.Another problem is the fact that there are frequently strong winds which drive small-sharp particles of sand into the plants,tearing and damaging them.The most difficult problem for all forms of plant life,however,is the fact that the entire annual rainfall occurs during a few days or weeks in spring.Grasses and flowers in desert survive from one year to the next by existing through the long, hot,dry season in the form of seeds.These seeds remain inactive unless the right amount of rain falls.If no rain falls,or if insufficient rain falls,they wait until the next year,or even still the next.Another factor that helps these plants to survive is the fact that their life cycles are short.By the time that the water from the spring rains disappears—ust a few weeks after it falls一such plants no longer need any.The perennials（多年生植物）have special features which enable them to survive as plants for several years. Thus,nearly all desert perennials have extensive root systems below ground and a small shoot system above ground.The large root network enables the plant to absorb as much water as possible in a short time.The small shoot system,on the other hand,considerably limits water loss by evaporation（蒸发）.Another feature of many desert perennials is that after the rainy season they lose their leaves in preparation for the long,dry season,just as trees in wetter climates lose theirs in preparation for the winter. This reduces their water loss by evaporation during the dry season.Then,in the next rainy season,they come fully alive once more,and grow new branches,leaves and flowers,just as the grasses and flowers in desert do.Ordinary plants can not survive the desert weather as a result of the following except for_________.A:the strong windsB:the strong sun's rayC:the long summer daysD:the high soil temperature
共用题干Plants in DesertOnly special plants can survive the terrible climate of a desert,for these are regions where the annual range of the soil temperature can be over 75℃．Furthermore,during the summer there are few clouds in the sky to protect plants from the sun's ray.Another problem is the fact that there are frequently strong winds that drive small,sharp particles of sand into the plants,tearing and damaging them.The most difficult problem for all forms of plant life,however,is the fact that the entire annual rainfall occurs during a few days or weeks in spring.Grasses and flowers in desert survive from one year to the next by existing through the long,hot,dry season in the form of seeds.These seeds remain inactive unless the right amount of rain falls.If no rain falls,or if insufficient rain falls,they wait until the next year,or even still the next.Another factor that helps these plants to survive is the fact that their life cycles are short.By the time the water from the spring rains disappears-just a few weeks after it falls-such plants no longer need any.The perennials（多年生植物）have special features that enable them to survive as plants for several years.Thus,nearly all desert perennials have extensive root systems below ground and a small shoot system above ground.The large root network enables the plant to absorb as much water as possible in short time.The small shoot system,on the other hand,considerably limits water loss by evaporation（蒸发）.Another feature of many perennials is that after the rainy season they lose their leaves in preparation for the long,dry season,just as trees in wetter climates lose theirs in preparation for the winter.This reduces their water loss by evaporation during the dry season.Then,in next rainy season,they come fully alive once more,and grow new branches,leaves and flowers,just as the grasses and flowers in desert do.A:Right B:Wrong C:Not mentioned
共用题干Plants in DesertOnly special plants can survive the terrible climate of a desert,for these are regions where the annual range of the soil temperature can be over 75℃．Furthermore,during the summer there are few clouds in the sky to protect plants from the sun's ray.Another problem is the fact that there are frequently strong winds that drive small,sharp particles of sand into the plants,tearing and damaging them.The most difficult problem for all forms of plant life,however,is the fact that the entire annual rainfall occurs during a few days or weeks in spring. Grasses and flowers in desert survive from one year to the next by existing through the long,hot,dry season in the form of seeds.These seeds remain inactive unless the right amount of rain falls.If no rain falls,or if insufficient rain falls,they wait until the next year,or even still the next.Another factor that helps these plants to survive is the fact that their life cycles are short.By the time the water from the spring rains disappears-just a few weeks after it falls-such plants no longer need any.The perennials（多年生植物）have special features that enable them to survive as plants for several years.Thus,nearly all desert perennials have extensive root systems below ground and a small shoot system above ground.The large root network enables the plant to absorb as much water as possible in short time. The small shoot system,on the other hand,considerably limits water ioss by evaporation（蒸发）.Another feature of many perennials is that after the rainy season they lose their leaves in preparation for the long,dry season,just as trees in wetter climates lose theirs in preparation for the winter.This reduces their water loss by evaporation during the dry season.Then,in next rainy season,they come fully alive once more,and grow new branches,leaves and flowers,just as the grasses and flowers in desert do.Grasses and flowers in the desert whose life cycles are short show their ability to adapt to the quick disappearance of rainwater there after it falls in spring.A:Right B:Wrong C:Not mentioned
共用题干The Northern LightsThe Sun is stormy and has its own kind of weather It is so hot and active that even the Sun's gravity cannot hold its atmosphere in check!Energy flows away from the Sun toward the Earth in a stream of electrified particles that move at speeds around a million miles per hour. These particles are called plasma,and the stream of plasma coming from the Sun is called the solar wind. The more active the Sun,the stronger the solar wind.The solar wind constantly streams toward the Earth,but don't worry because a protective magnetic field surrounds our planet.The same magnetic field that makes your compass point north also steers the particles from the Sun to the north and south poles.The charged particles become trapped in magnetic belts around the Earth. When a large blast of solar wind crashes into the Earth's magnetic field,the magnetic field first gets squeezed and then the magnetic field lines break and reconnect.The breaking and reconnecting of the magnetic field lines can cause atomic particles called electrons trapped in the belts to fall into the Earth's atmosphere at the poles. As the electrons fall to the Earth,they collide with gas molecules in the atmosphere,creating flashes of light in the sky. Each atmospheric gas glows a different color. Oxygen and nitrogen glows red and green and nitrogen glows violet-purple. As these various colors glow and dance in the night sky,they create the Northern Lights and the Southern Lights.Watching auroras is fun and exciting,but normally you can only see them in places far north like Alaska and Canada. The movement of the aurora across the sky is usually slow enough to easily follow with your eyes but they can also pulsate,flicker,or even move like waves.During solar maximum,auroras are seen as far south as Florida,even Mexico!Auroras often seem to be very close to the ground,but the lowest aurora is still about 100 kilometers above the ground,a distance much higher than clouds are formed or airplanes can fly. A typical aurora band can be thousands of kilometers long,a few hundred kilometers high,but only a few hundred meters thick.We hope you are able to travel to far north places like the Arctic Circle and see the Northern Lights at least once during your lifetime. We know you will never forget it!Some scientists are worrying about the possible disappearance of the Earth's protective magnetic field in the future.A: RightB: WrongC: Not mentioned
Geothermal(地热)Energy 1 Since heat naturally moves from hotter regions to cooler ones, the heat from the earth's center flows outwards towards the surface. In this way, it transfers to the next layer of rock. If the temperature is high enough, some of this rock melts and forms magma(岩浆). The magma ascends in its turn towards the earth's surface. It often remains well below the earth's surface, creating vast areas of hot rock. In such regions, there are deep cracks, which allow rainwater to descend underground. Some of the heated rainwater travels back up to the earth's surface where it will appear as a hot spring. However, if this ascending hot water reaches a layer of impermeable(不可渗透的)rock, it remains trapped, forming a geothermal reservoir. If geothermal reservoirs are close enough to the surface, they can be reached by drilling wells. Hot water and steam shoot up the wells naturally, and can be used to produce electricity in geothermal power plants. 2.A few geothermal power plants depend on dry-stem reservoirs which produce steam but little or no water. In these cases, the steam is piped up directly to provide the power to spin a turbine generator. The first geothermal power plant, constructed at Lardarello in Italy, was of this type, and is still producing electricity today. 3.Most currently operating geothermal power plants are either "flash" steam plants or binary(双重的)plants. Flash plants produce mainly hot water ranging in temperature from 300° to 700°Fahrenheit. This water is passed through one or two separators where released from the pressure of the underground reservoir, it "flashes" or boils into steam Again, the force of this steam provides the energy to spin the turbine and produce electricity. The geothermal water and steam are then reinjected directly back down into the earth to maintain the volume and pressure of the reservoir. Gradually they will be reheated and can then be used again. 4.A reservoir with temperatures below 300° Fahrenheit is not hot enough to flash steam but it can still be used to generate electricity in binary fluid. The steam from this is used to power the turbines. As in the flash steam plant, the geothermal water is recycled back into the reservoir.文章(23~30)Paragraph1_____A.Dry steam plantsB.Binary plantsC.Origin of geothermal energyD.Generation of electricityE.Flash steam plantsF.Recyclable water and steam
共用题干Plants in DesertOnly special plants can survive the terrible climate of a desert,for these are regions where the annual range of the soil temperature can be over 75℃．Furthermore,during the summer there are few clouds in the sky to protect plants from the sun's ray.Another problem is the fact that there are frequently strong winds that drive small,sharp particles of sand into the plants,tearing and damaging them.The most difficult problem for all forms of plant life,however,is the fact that the entire annual rainfall occurs during a few days or weeks in spring. Grasses and flowers in desert survive from one year to the next by existing through the long,hot,dry season in the form of seeds.These seeds remain inactive unless the right amount of rain falls.If no rain falls,or if insufficient rain falls,they wait until the next year,or even still the next.Another factor that helps these plants to survive is the fact that their life cycles are short.By the time the water from the spring rains disappears-just a few weeks after it falls-such plants no longer need any.The perennials（多年生植物）have special features that enable them to survive as plants for several years.Thus,nearly all desert perennials have extensive root systems below ground and a small shoot system above ground.The large root network enables the plant to absorb as much water as possible in short time. The small shoot system,on the other hand,considerably limits water ioss by evaporation（蒸发）.Another feature of many perennials is that after the rainy season they lose their leaves in preparation for the long,dry season,just as trees in wetter climates lose theirs in preparation for the winter.This reduces their water loss by evaporation during the dry season.Then,in next rainy season,they come fully alive once more,and grow new branches,leaves and flowers,just as the grasses and flowers in desert do.Ordinary plants are unable to survive in the desert mainly because of the changeable weather.A:Right B:Wrong C:Not mentioned
共用题干Plants in DesertOnly special plants can survive the terrible climate of a desert,for these are regions where the annual range of the soil temperature can be over 75℃．Furthermore,during the summer there are few clouds in the sky to protect plants from the sun's ray.Another problem is the fact that there are frequently strong winds that drive small,sharp particles of sand into the plants,tearing and damaging them.The most difficult problem for all forms of plant life,however,is the fact that the entire annual rainfall occurs during a few days or weeks in spring. Grasses and flowers in desert survive from one year to the next by existing through the long,hot,dry season in the form of seeds.These seeds remain inactive unless the right amount of rain falls.If no rain falls,or if insufficient rain falls,they wait until the next year,or even still the next.Another factor that helps these plants to survive is the fact that their life cycles are short.By the time the water from the spring rains disappears-just a few weeks after it falls-such plants no longer need any.The perennials（多年生植物）have special features that enable them to survive as plants for several years.Thus,nearly all desert perennials have extensive root systems below ground and a small shoot system above ground.The large root network enables the plant to absorb as much water as possible in short time. The small shoot system,on the other hand,considerably limits water ioss by evaporation（蒸发）.Another feature of many perennials is that after the rainy season they lose their leaves in preparation for the long,dry season,just as trees in wetter climates lose theirs in preparation for the winter.This reduces their water loss by evaporation during the dry season.Then,in next rainy season,they come fully alive once more,and grow new branches,leaves and flowers,just as the grasses and flowers in desert do.The shoot system of perennials can help the plants absorb less of the sun's ray.A:Right B:Wrong C:Not mentioned
共用题干Plants in DesertOnly special plants can survive the terrible climate of a desert,for these are regions where the annual range of the soil temperature can be over 75℃．Furthermore,during the summer there are few clouds in the sky to protect plants from the sun's ray.Another problem is the fact that there are frequently strong winds that drive small,sharp particles of sand into the plants,tearing and damaging them.The most difficult problem for all forms of plant life,however,is the fact that the entire annual rainfall occurs during a few days or weeks in spring. Grasses and flowers in desert survive from one year to the next by existing through the long,hot,dry season in the form of seeds.These seeds remain inactive unless the right amount of rain falls.If no rain falls,or if insufficient rain falls,they wait until the next year,or even still the next.Another factor that helps these plants to survive is the fact that their life cycles are short.By the time the water from the spring rains disappears-just a few weeks after it falls-such plants no longer need any.The perennials（多年生植物）have special features that enable them to survive as plants for several years.Thus,nearly all desert perennials have extensive root systems below ground and a small shoot system above ground.The large root network enables the plant to absorb as much water as possible in short time. The small shoot system,on the other hand,considerably limits water ioss by evaporation（蒸发）.Another feature of many perennials is that after the rainy season they lose their leaves in preparation for the long,dry season,just as trees in wetter climates lose theirs in preparation for the winter.This reduces their water loss by evaporation during the dry season.Then,in next rainy season,they come fully alive once more,and grow new branches,leaves and flowers,just as the grasses and flowers in desert do.Winter is the toughest season for the grasses and flowers to surviVe.A:Right B:Wrong C:Not mentioned
共用题干第一篇The Northern LightsThe sun is stormy and has its own kind of weather.It is so hot and active that even the Sun's gravity cannot hold its atmosphere in check!Energy flows away from the Sun toward the Earth in a stream of electrified particles that move at speeds around a million miles per hour.These particles are called plasma （等离子体）,and the stream of plasma coming from the Sun is called the solar wind.The more active the Sun,the stronger the solar wind.The solar wind constantly streams toward the Earth,but don't worry because a protective magnetic field surrounds our planet.The same magnetic field that makes your compass point north also steers the particles from the Sun to the north and south poles.The charged particles become trapped in magnetic belts around the Earth.When a large blast of solar wind crashes into the Earth's magnetic field,the magnetic field first gets squeezed and then the magnetic field lines break and reconnect.The breaking and reconnecting of the magnetic field lines can cause atomic particles called electrons trapped in the belts to fall into tile Earth's atmosphere at the poles.As the electrons fall to the Earth,they collide with gas molecules in the atmosphere,creating flashes of light in the sky.Each atmospheric gas glows a different color.Oxygen and nitrogen glows red and green arid nitrogen glows violet purple.As these various colors glow and dance in the night sky,they create the Northern Lights and the Southern Lights.Watching auroras（北极光）is fun and exciting, but normally you can only see them in places far north like Alaska and Canada.The movement of the aurora across the sky is usually slow enough to easily follow with your eyes but they can also pulsate（跳动）,flicker（闪烁）,or even move like waves.During solar maximum,5 auroras are seen as far south as Florida,even Mexico!Auroras often seem to be very close to the ground,but the lowest aurora is still about 100 kilometers above the ground,a distance much higher than clouds are formed or airplanes can fly.A typical aurora band can be thousands of kilometers long,a few hundred kilometers high,but only a few hundred meters thick.We hope you are able to travel to far north places like the Arctic Circle and see the Northern Lights at least once during your lifetime.We know you will never forget it!The solar wind comes into being as a result of_______.A:disappearance of the Sun's gravityB:unpredictable weather of the SunC:fast flow of energy away from the SunD:a stream of particles being blown away
共用题干The Northern LightsThe Sun is stormy（狂暴的）and has its own kind of weather. It is so hot and active that even the Sun ' s gravity cannot hold its atmosphere in check（控制，支配）!Energy flows away from the Sun toward the Earth in a stream of electrified particles（电粒子）that move at speeds around a million miles per hour. These path- dles are called plasma（等离子体）, and the stream of plasma coming from the Sun is called the solar wind. The more active the Sun,the stronger the solar wind.The solar wind constantly streams toward the Earth,but don't worry because a protective magnetic field （磁场）surrounds our planet. The same magnetic field that makes your compass point north also steer（引导）the particles from the Sun to the north and south poles.The charged particles become trapped in magnetic belts around the Earth.When a large blast of solar wind crashes into the Earth's magnetic field,the magnetic field first gets squeezed and then the magnetic field lines break and reconnect.The breaking and reconnecting of the magnetic field lines can cause atomic particles（原子粒子）called electrons（电子）trapped in the belts to fall into the Earth ' s atmosphere at the poles. As the electrons fall to the Earth,they collide with gas molecules（分子）in the atmosphere,creating flashes of light in the sky. Each atmospheric gas glows a different color. Oxygen and nitrogen glow red and green and nitrogen glows violet- purple. As these various colors glow and dance in the night sky,they create the Northern Lights and the Southern Lights.Watching auroras is fun and exciting,but normally you can only see them in places far north like Alaska and Canada. The movement of the aurora across the sky is usually slow enough to easily follow with your eyes but they can also pulsate（跳动）,flicker,or even move like waves. During solar maximum,auroras are seen as far south as Florida,even Mexico!Auroras often seem to be very close to the ground,but the lowest aurora is still about 100 kilometers above the ground,a distance much higher than clouds are formed or airplanes can fly.A typical aurora band can be thousands of kilometers long,a few hundred kilometers high,but only a few hundred meters thick.We hope you are able to travel to far-north places like the Arctic Circle and see the Northern Lights at least once during your lifetime.We know you will never forget it!You cannot see the Northern Lights unless you are in Alaska or Canada.A:RightB:WrongC:Not mentioned
共用题干The Northern LightsThe Sun is stormy and has its own kind of weather It is so hot and active that even the Sun's gravity cannot hold its atmosphere in check!Energy flows away from the Sun toward the Earth in a stream of electrified particles that move at speeds around a million miles per hour. These particles are called plasma,and the stream of plasma coming from the Sun is called the solar wind. The more active the Sun,the stronger the solar wind.The solar wind constantly streams toward the Earth,but don't worry because a protective magnetic field surrounds our planet.The same magnetic field that makes your compass point north also steers the particles from the Sun to the north and south poles.The charged particles become trapped in magnetic belts around the Earth. When a large blast of solar wind crashes into the Earth's magnetic field,the magnetic field first gets squeezed and then the magnetic field lines break and reconnect.The breaking and reconnecting of the magnetic field lines can cause atomic particles called electrons trapped in the belts to fall into the Earth's atmosphere at the poles. As the electrons fall to the Earth,they collide with gas molecules in the atmosphere,creating flashes of light in the sky. Each atmospheric gas glows a different color. Oxygen and nitrogen glows red and green and nitrogen glows violet-purple. As these various colors glow and dance in the night sky,they create the Northern Lights and the Southern Lights.Watching auroras is fun and exciting,but normally you can only see them in places far north like Alaska and Canada. The movement of the aurora across the sky is usually slow enough to easily follow with your eyes but they can also pulsate,flicker,or even move like waves.During solar maximum,auroras are seen as far south as Florida,even Mexico!Auroras often seem to be very close to the ground,but the lowest aurora is still about 100 kilometers above the ground,a distance much higher than clouds are formed or airplanes can fly. A typical aurora band can be thousands of kilometers long,a few hundred kilometers high,but only a few hundred meters thick.We hope you are able to travel to far north places like the Arctic Circle and see the Northern Lights at least once during your lifetime. We know you will never forget it!Tens of thousands of tourists take special trips to Norway and Sweden every year to watch the Northern Lights.A: RightB: WrongC: Not mentioned
共用题干Plants in DesertOnly special plants can survive the terrible climate of a desert,for these are regions where the annual range of the soil temperature can be over 75℃．Furthermore,during the summer there are few clouds in the sky to protect plants from the sun's ray.Another problem is the fact that there are frequently strong winds that drive small,sharp particles of sand into the plants,tearing and damaging them.The most difficult problem for all forms of plant life,however,is the fact that the entire annual rainfall occurs during a few days or weeks in spring. Grasses and flowers in desert survive from one year to the next by existing through the long,hot,dry season in the form of seeds.These seeds remain inactive unless the right amount of rain falls.If no rain falls,or if insufficient rain falls,they wait until the next year,or even still the next.Another factor that helps these plants to survive is the fact that their life cycles are short.By the time the water from the spring rains disappears-just a few weeks after it falls-such plants no longer need any.The perennials（多年生植物）have special features that enable them to survive as plants for several years.Thus,nearly all desert perennials have extensive root systems below ground and a small shoot system above ground.The large root network enables the plant to absorb as much water as possible in short time. The small shoot system,on the other hand,considerably limits water ioss by evaporation（蒸发）.Another feature of many perennials is that after the rainy season they lose their leaves in preparation for the long,dry season,just as trees in wetter climates lose theirs in preparation for the winter.This reduces their water loss by evaporation during the dry season.Then,in next rainy season,they come fully alive once more,and grow new branches,leaves and flowers,just as the grasses and flowers in desert do.The theme of the second last paragraph is why the perennials can survive as plants for several years.A:Right B:Wrong C:Not mentioned
共用题干Plants in DesertOnly special plants can survive the terrible climate of a desert,for these are regions where the annual range of the soil temperature can be over 75℃．Furthermore,during the summer there are few clouds in the sky to protect plants from the sun's ray.Another problem is the fact that there are frequently strong winds that drive small,sharp particles of sand into the plants,tearing and damaging them.The most difficult problem for all forms of plant life,however,is the fact that the entire annual rainfall occurs during a few days or weeks in spring. Grasses and flowers in desert survive from one year to the next by existing through the long,hot,dry season in the form of seeds.These seeds remain inactive unless the right amount of rain falls.If no rain falls,or if insufficient rain falls,they wait until the next year,or even still the next.Another factor that helps these plants to survive is the fact that their life cycles are short.By the time the water from the spring rains disappears-just a few weeks after it falls-such plants no longer need any.The perennials（多年生植物）have special features that enable them to survive as plants for several years.Thus,nearly all desert perennials have extensive root systems below ground and a small shoot system above ground.The large root network enables the plant to absorb as much water as possible in short time. The small shoot system,on the other hand,considerably limits water ioss by evaporation（蒸发）.Another feature of many perennials is that after the rainy season they lose their leaves in preparation for the long,dry season,just as trees in wetter climates lose theirs in preparation for the winter.This reduces their water loss by evaporation during the dry season.Then,in next rainy season,they come fully alive once more,and grow new branches,leaves and flowers,just as the grasses and flowers in desert do.Desert perennials lose their leaves after the rainy season just as trees in wetter climates lose theirs because winter arrives,but the reasons for this feature are different.A:Right B:Wrong C:Not mentioned
共用题干Plants in DesertOnly special plants can survive the terrible climate of a desert,for these are regions where the annual range of the soil temperature can be over 75℃．Furthermore,during the summer there are few clouds in the sky to protect plants from the sun's ray.Another problem is the fact that there are frequently strong winds that drive small,sharp particles of sand into the plants,tearing and damaging them.The most difficult problem for all forms of plant life,however,is the fact that the entire annual rainfall occurs during a few days or weeks in spring. Grasses and flowers in desert survive from one year to the next by existing through the long,hot,dry season in the form of seeds.These seeds remain inactive unless the right amount of rain falls.If no rain falls,or if insufficient rain falls,they wait until the next year,or even still the next.Another factor that helps these plants to survive is the fact that their life cycles are short.By the time the water from the spring rains disappears-just a few weeks after it falls-such plants no longer need any.The perennials（多年生植物）have special features that enable them to survive as plants for several years.Thus,nearly all desert perennials have extensive root systems below ground and a small shoot system above ground.The large root network enables the plant to absorb as much water as possible in short time. The small shoot system,on the other hand,considerably limits water ioss by evaporation（蒸发）.Another feature of many perennials is that after the rainy season they lose their leaves in preparation for the long,dry season,just as trees in wetter climates lose theirs in preparation for the winter.This reduces their water loss by evaporation during the dry season.Then,in next rainy season,they come fully alive once more,and grow new branches,leaves and flowers,just as the grasses and flowers in desert do.Grasses and flowers in desert are able to survive because they stay in the form of seeds to wait for the right amount of water to come.A:Right B:Wrong C:Not mentioned
共用题干The Northern LightsThe Sun is stormy and has its own kind of weather It is so hot and active that even the Sun's gravity cannot hold its atmosphere in check!Energy flows away from the Sun toward the Earth in a stream of electrified particles that move at speeds around a million miles per hour. These particles are called plasma,and the stream of plasma coming from the Sun is called the solar wind. The more active the Sun,the stronger the solar wind.The solar wind constantly streams toward the Earth,but don't worry because a protective magnetic field surrounds our planet.The same magnetic field that makes your compass point north also steers the particles from the Sun to the north and south poles.The charged particles become trapped in magnetic belts around the Earth. When a large blast of solar wind crashes into the Earth's magnetic field,the magnetic field first gets squeezed and then the magnetic field lines break and reconnect.The breaking and reconnecting of the magnetic field lines can cause atomic particles called electrons trapped in the belts to fall into the Earth's atmosphere at the poles. As the electrons fall to the Earth,they collide with gas molecules in the atmosphere,creating flashes of light in the sky. Each atmospheric gas glows a different color. Oxygen and nitrogen glows red and green and nitrogen glows violet-purple. As these various colors glow and dance in the night sky,they create the Northern Lights and the Southern Lights.Watching auroras is fun and exciting,but normally you can only see them in places far north like Alaska and Canada. The movement of the aurora across the sky is usually slow enough to easily follow with your eyes but they can also pulsate,flicker,or even move like waves.During solar maximum,auroras are seen as far south as Florida,even Mexico!Auroras often seem to be very close to the ground,but the lowest aurora is still about 100 kilometers above the ground,a distance much higher than clouds are formed or airplanes can fly. A typical aurora band can be thousands of kilometers long,a few hundred kilometers high,but only a few hundred meters thick.We hope you are able to travel to far north places like the Arctic Circle and see the Northern Lights at least once during your lifetime. We know you will never forget it!The Earth is quite safe with a magnetic field surrounding it to protect it from the attack by the solar wind.A: RightB: WrongC: Not mentioned
共用题干第一篇Plant GasScientists have been studying natural sources of methane（甲烷，沼气）for decades but hadn't regarded plants as a producer, notes Frank Keppler, a geochemist（地球化学家）at the Max Planck Institute for Nuclear Physics in Heldelberg,Germany. Now Keppler and his colleagues find that plants,from grasses to trees,may also be sources of the greenhouse gas.This is really surprising, because most scientists assumed that methane production requires an oxygen-free environment.Previously,researchers had thought that it was impossible for plants to make significant amounts of the gas. They had assumed that microbes（微生物）need to be in environments without oxygen to produce methane.Methane is a greenhouse gas, like carbon dioxide.Gases such as methane and carbon dioxide trap heat in Earth's atmosphere and contribute to global warming.In its experiments, Keppler's team used sealed chambers（室，房间；腔）that contained the same concentration of oxygen that Earth's atmosphere has.They measured the amounts of methane that were released by both living plants and dried plant material,such as fallen leaves.With the dried plants,the researchers took measurement at temperatures ranging from 30 degrees Celsius to 70 degrees C.At 30 degrees C.,they found,a gram of dried plant material released up to 3 nanograms（微克）of methane per hour(One nanogram is a millionth of a gram). With every 10-degree rise in temperature,the amount of methane released each hour roughly doubled.Living plants growing at their normal temperatures released as much as 370 nanograms of methane per gram of plant tissue per hour. Methane emissions tripled when living and dead plant was exposed to sunlight.Because there was plenty of oxygen available,it's unlikely that the types of bacteria(bacterium的复数，细菌）that normally make methane were involved. Experiments on plants that were grown in water rather than soil also resulted in methane emissions.That's another strong sign that the gas came from the plants and not soil microbes.The new finding is an"interesting observation,"says Jennifer Y. King,a biogeochemist（生物地球化学家）at the University of Minnesota in St. Paul. Because some types of soil microbes consume methane,they may prevent plant-produced methane from reaching the atmosphere.Field tests will be needed to assess the plant's influence,she notes.Which statement is true of the methane emissions of plants in the experiment?A:The lower the temperature,the higher the amount of methane emissions.B:Living plants release less methane than dried plants at the same temperature.C:When exposed to sunlight,plants stop releasing methane.D:The higher the temperature,the greater the amount of methane emissions.
共用题干第一篇The Northern LightsThe sun is stormy and has its own kind of weather.It is so hot and active that even the Sun's gravity cannot hold its atmosphere in check!Energy flows away from the Sun toward the Earth in a stream of electrified particles that move at speeds around a million miles per hour.These particles are called plasma （等离子体）,and the stream of plasma coming from the Sun is called the solar wind.The more active the Sun,the stronger the solar wind.The solar wind constantly streams toward the Earth,but don't worry because a protective magnetic field surrounds our planet.The same magnetic field that makes your compass point north also steers the particles from the Sun to the north and south poles.The charged particles become trapped in magnetic belts around the Earth.When a large blast of solar wind crashes into the Earth's magnetic field,the magnetic field first gets squeezed and then the magnetic field lines break and reconnect.The breaking and reconnecting of the magnetic field lines can cause atomic particles called electrons trapped in the belts to fall into tile Earth's atmosphere at the poles.As the electrons fall to the Earth,they collide with gas molecules in the atmosphere,creating flashes of light in the sky.Each atmospheric gas glows a different color.Oxygen and nitrogen glows red and green arid nitrogen glows violet purple.As these various colors glow and dance in the night sky,they create the Northern Lights and the Southern Lights.Watching auroras（北极光）is fun and exciting, but normally you can only see them in places far north like Alaska and Canada.The movement of the aurora across the sky is usually slow enough to easily follow with your eyes but they can also pulsate（跳动）,flicker（闪烁）,or even move like waves.During solar maximum,5 auroras are seen as far south as Florida,even Mexico!Auroras often seem to be very close to the ground,but the lowest aurora is still about 100 kilometers above the ground,a distance much higher than clouds are formed or airplanes can fly.A typical aurora band can be thousands of kilometers long,a few hundred kilometers high,but only a few hundred meters thick.We hope you are able to travel to far north places like the Arctic Circle and see the Northern Lights at least once during your lifetime.We know you will never forget it!The Northern Lights are created when_______.A:the magnetic field lines fail to reconnectB:the electrons falling to the Earth shine in different colorsC:atomic particles fall to the Earth and collide with atmospheric gas moleculesD:oxygen and nitrogen are separated from the atmospheric gases
共用题干The Northern LightsThe Sun is stormy and has its own kind of weather It is so hot and active that even the Sun's gravity cannot hold its atmosphere in check!Energy flows away from the Sun toward the Earth in a stream of electrified particles that move at speeds around a million miles per hour. These particles are called plasma,and the stream of plasma coming from the Sun is called the solar wind. The more active the Sun,the stronger the solar wind.The solar wind constantly streams toward the Earth,but don't worry because a protective magnetic field surrounds our planet.The same magnetic field that makes your compass point north also steers the particles from the Sun to the north and south poles.The charged particles become trapped in magnetic belts around the Earth. When a large blast of solar wind crashes into the Earth's magnetic field,the magnetic field first gets squeezed and then the magnetic field lines break and reconnect.The breaking and reconnecting of the magnetic field lines can cause atomic particles called electrons trapped in the belts to fall into the Earth's atmosphere at the poles. As the electrons fall to the Earth,they collide with gas molecules in the atmosphere,creating flashes of light in the sky. Each atmospheric gas glows a different color. Oxygen and nitrogen glows red and green and nitrogen glows violet-purple. As these various colors glow and dance in the night sky,they create the Northern Lights and the Southern Lights.Watching auroras is fun and exciting,but normally you can only see them in places far north like Alaska and Canada. The movement of the aurora across the sky is usually slow enough to easily follow with your eyes but they can also pulsate,flicker,or even move like waves.During solar maximum,auroras are seen as far south as Florida,even Mexico!Auroras often seem to be very close to the ground,but the lowest aurora is still about 100 kilometers above the ground,a distance much higher than clouds are formed or airplanes can fly. A typical aurora band can be thousands of kilometers long,a few hundred kilometers high,but only a few hundred meters thick.We hope you are able to travel to far north places like the Arctic Circle and see the Northern Lights at least once during your lifetime. We know you will never forget it!An aurora is generally close to the ground and is very long and thick.A: RightB: WrongC: Not mentioned
共用题干第三篇Citizen ScientistsUnderstanding how nature responds to climate change will require monitoring key life cycle events一 flowering,the appearance of leaves and the first frog calls of the spring一all around the world.But ecologists can't be everywhere so they're turning to non-scientists,sometimes called citizen scientists,for help.Climate scientists are not present everywhere.Because there are so many places in the world and not enough scientists to observe all of them,they're asking for your help in observing signs of climate change across the world.The citizen scientist movement encourages ordinary people to observe a very specificresearch interest一birds,trees,flowers budding,etc.and send their observations to a giant database to be observed by professional scientists.This helps a small number of scientists track a large amount of data that they would never be able to gather on their own.Much like citizen journalists helping large publications cover a hyper-local beat,citizen scientists are ready for the conditions where they live in.All that's needed to become one is a few minutes each day or each week to gather data and send them in.A group of scientists and educators launched an organization last year called the National Phenology Network."Phenology"is what scientists call the study of the timing of events in nature.One of the group's first efforts relies on scientists and non-scientists alike to collect data about plant flowering and leafing eveiy year.The program,called Project BudBurst,collects life cycle data on a variety of common plants from across the United States.People participating in the project一which is open to every- one一record their observations on the Project BudBurst website."People don't have to be plant experts一they just have to look around and see what's in their neighbor- hood,"says Jennifer Schwartz,an education consultant with the project."As we collect these data,we'll be able to make an estimate of how plants and communities of plants and animals will respond as the climatechanges."What is the final purpose of Project BudBurst?A:To study when plants will have their first buds.B:To find out the types of plants in the neighborhood.C:To collect life cycle data on a variety of common plants from across the United States.D:To investigate how plants and animals will respond as the climate changes.
共用题干第三篇Citizen ScientistsUnderstanding how nature responds to climate change will require monitoring key life cycle events一 flowering,the appearance of leaves and the first frog calls of the spring一all around the world.But ecologists can't be everywhere so they're turning to non-scientists,sometimes called citizen scientists,for help.Climate scientists are not present everywhere.Because there are so many places in the world and not enough scientists to observe all of them,they're asking for your help in observing signs of climate change across the world.The citizen scientist movement encourages ordinary people to observe a very specificresearch interest一birds,trees,flowers budding,etc.and send their observations to a giant database to be observed by professional scientists.This helps a small number of scientists track a large amount of data that they would never be able to gather on their own.Much like citizen journalists helping large publications cover a hyper-local beat,citizen scientists are ready for the conditions where they live in.All that's needed to become one is a few minutes each day or each week to gather data and send them in.A group of scientists and educators launched an organization last year called the National Phenology Network."Phenology"is what scientists call the study of the timing of events in nature.One of the group's first efforts relies on scientists and non-scientists alike to collect data about plant flowering and leafing eveiy year.The program,called Project BudBurst,collects life cycle data on a variety of common plants from across the United States.People participating in the project一which is open to every- one一record their observations on the Project BudBurst website."People don't have to be plant experts一they just have to look around and see what's in their neighbor- hood,"says Jennifer Schwartz,an education consultant with the project."As we collect these data,we'll be able to make an estimate of how plants and communities of plants and animals will respond as the climatechanges."What is NOT true of Project BudBurst?A:Only experts can participate in it.B:Everybody can participate in it.C:It collects life cycle data on a variety of common plants.D:It has its own website.
多选题Consider each of the choices separately and select all that apply. Which of these can be inferred from the fact that the French built orangeries for certain tropical plants?AGreenhouses may be used to keep plants at a moderate temperatureBThe climate of France is unsuited to growing tropical plants outdoors.CLouis ⅩⅣ was a frequent and enthusiastic traveler to Africa and Asia
问答题Practice 3 At first, as he adjusted pumps and checked temperatures, Aaron Boucher looked like any technician in the control room of an electrical plant. Then he rushed to the window and scanned the sky, to check his fuel supply. Mr. Boucher was battling clouds, timing the operations of his power plant to get the most out of patchy sunshine. It is a skill that may soon be in greater demand, for the world appears to be on the verge of a boom in a little-known but promising type of solar power. It is not the kind that features shiny panels bolted to the roofs of houses. This type involves covering acres of desert with mirrors that focus intense sunlight on a fluid, heating it enough to make steam. The steam turns a turbine and generates electricity. The technology is not new, but it is suddenly in high demand. As prices rise for fossil fuels and worries grow about their contribution to global warming, solar thermal plants are being viewed as a renewable power source with huge potential. After a decade of no activity, two prototype solar thermal plants were recently opened in the United States, with a capacity that could power several big hotels, neon included, on the Las Vegas Strip, about 20 miles north of here. Another 10 power plants are in advanced planning in California, Arizona and Nevada. On sunny afternoons, those 10 plants would produce as much electricity as three nuclear reactors, but they can be built in as little as two years, compared with a decade or longer for a nuclear plant. Some of the new plants will feature systems that allow them to store heat and generate electricity for hours after sunset. At Nevada Solar One the other day, Mr. Boucher, 30, ran the computerized control room. He was trying to produce as much electricity as possible while saving heat to tide the plant over as clouds cast episodic shadows on the solar array. “I’ve been fighting it all day,” he said. Imperceptibly, in the dusty wind of the high desert, 182,000 mirrors moved from east to west, tracking the sun across the sky.