单选题If a small electric motor is immersed in salt water it should be （） (1) washed in fresh water (2) dried in an ovenA(1) onlyB(2) onlyCboth (1) and (2)Dneither (1) or (2)
单选题
If a small electric motor is immersed in salt water it should be （） (1) washed in fresh water (2) dried in an oven
A
(1) only
B
(2) only
C
both (1) and (2)
D
neither (1) or (2)
参考解析
解析：
暂无解析
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请阅读短文，完成此题。When we analyze the salt salinity(盐溶度 ) of ocean waters, we find that it varies only slightly from place to place. Nevertheless, some of these small changes are important. There are three basic processes that cause a change in oceanic salinity. One of these is the subtraction of water from the ocean by means of evaporation. In this manner, the salinity is increased, since the salt stays behind. If this is carried to the extreme, of course, white salt would be left behind; this, by the way, is how much of the table salt we use is actually obtained.The opposite of evaporation is precipitation, such as rain, by which water is added to the ocean. Here the ocean is being diluted so that the salinity is decreased. This may occur in areas ofhigh rainfall or in coastal regions where rivers flow into the ocean. Thus salinity may be increased by the subtraction of water by-evaporation, or decreased by the addition of fresh water by precipitation.Normally, in hot regions where the sun is very strong, the ocean salinity is somewhat higher than it is in other parts of the world where there is not as much evaporation. Similarly, in coastal regions where rivers dilute the sea, salinity is somewhat lower than in other oceanic areas.A third process by which salinity may be altered is associated with the formation and melting of sea ice. When seawater is frozen, the dissolved materials are left behind. In this manner, seawater directly beneath freshly formed sea ice has a higher salinity than it did before the ice appeared. Of course, when this ice melts, it will tend to decrease the salinity of the surrounding water.In the Weddell Sea, the densest water in the ocean is formed as a result of this freezing process, which increases the salinity of cold water. This heavy water sinks and is found in the deeper portion of the oceans of the world.It can be known from the passage that increase in the salinity of ocean water is caused by__________.查看材料A．melting of sea iceB．precipitationC．evaporationD．supplement of salt
共用题干Where Has the Salt Come from?Every now and then,we meet a fact about our earth that makes us feel strange and no answer for the fact has yet been found.Such a fact is the existence of salt in the oceans. How did it get there?We simply do not know how the salt got into the ocean!We do know,of course,that salt is water-soluble,and so passes into the oceans with rainwater.The salt of the earth's surface is constantly being dissolved（溶解）and is passing into the ocean.But we do not know whether this can explain the huge quantity of salt in oceans.If all the oceans were dried up,enough salt would be left to build a wall 180 miles high and a mile thick. Such a wall would reach once around the world at the Equator（赤道）!The common salt that we all use is produced from seawater or the water of salt lakes, from salt springs（源泉）and from deposits of rock salt. The concentration（浓度）of salt in seawater ranges from about three percent to three-and-one-half percent. The Dead Sea, which covers an area of about 340 square miles,contains about 11,600,000,000 tons of salt!On the average, a gallon（加仑）of seawater contains about a quarter of a pound of salt.The beds of rock salt that are found in various parts of the world were all originally formed by the evaporation（蒸发）of seawater millions of years ago. It is believed that the thick rock-salt deposits were formed after about nine-tenth of theY volume of seawater had been evaporated.Most commercial salt is obtained from rock salt.The usual method is to drill wells（井） down to the salt beds. Pure water is pumped down（抽进去）through a pipe. The water dissolves the salt and it is forced through another pipe up to the surface.A:Right B:Wrong C:Not mentioned
共用题干Where Has the Salt Come from?Every now and then,we meet a fact about our earth that makes us feel strange and no answer for the fact has yet been found.Such a fact is the existence of salt in the oceans. How did it get there?We simply do not know how the salt got into the ocean!We do know,of course,that salt is water-soluble,and so passes into the oceans with rainwater.The salt of the earth's surface is constantly being dissolved（溶解）and is passing into the ocean.But we do not know whether this can explain the huge quantity of salt in oceans.If all the oceans were dried up,enough salt would be left to build a wall 180 miles high and a mile thick. Such a wall would reach once around the world at the Equator（赤道）!The common salt that we all use is produced from seawater or the water of salt lakes, from salt springs（源泉）and from deposits of rock salt. The concentration（浓度）of salt in seawater ranges from about three percent to three-and-one-half percent. The Dead Sea, which covers an area of about 340 square miles,contains about 11,600,000,000 tons of salt!On the average, a gallon（加仑）of seawater contains about a quarter of a pound of salt.The beds of rock salt that are found in various parts of the world were all originally formed by the evaporation（蒸发）of seawater millions of years ago. It is believed that the thick rock-salt deposits were formed after about nine-tenth of theY volume of seawater had been evaporated.Most commercial salt is obtained from rock salt.The usual method is to drill wells（井） down to the salt beds. Pure water is pumped down（抽进去）through a pipe. The water dissolves the salt and it is forced through another pipe up to the surface.Beds of rock salt are found in every part of the world.A:Right B:Wrong C:Not mentioned
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单选题Passage2 Questions 6 to 10 are based on the following passage. Salt is as necessary to life as water. In many areas of Africa people once drank the urine（尿）of animals because they had no other source of salt. Without salt, human beings die. The human body demands that the amount of salt in the blood always stay the same. When the body does not get enough salt, it protects itself by letting less salt leave the body in. urine and sweat. But it cannot reduce this output to zero. Some salt is always escaping. On a completely saltless diet, like that of some people in Africa, the body steadily loses small amounts of salt through the kidneys（肾） and sweat glands(腺). It then tries to adjust to this loss by speeding up its secretion(分泌) of water. (78) In this way, the body attempts to keep the amount of salt in the blood at the necessary level. The result is a slow drying up of body and, finally, death. The person dies of thirst. In cases where there is little or no water to drink, the body tries to do the opposite thing.Again, it must keep the salt level in the blood constant. Because it has little water, it attempts to stop water from leaving the body and to increase its secretion of. salt. But, as with the escaping salt, it cannot be completely successful. Some water still leaves and the person eventually dies of thirst. In short, the body's normal needs for salt and for water are both parts of the same important need to keep the salt level in the blood constant.6 Some African people once drank animal urine______.Awhen they were going to dieBbecause they were thirstyCbecause there was little saltDbecause they were short of water
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