单选题Why does land become desert after all trees are cut down?ABecause nothing remains on land except floods.BBecause there are no longer trees to keep the rain and protect the top-soil.CBecause too much rain sinks in and washes away the top-soil.DBecause roots of the trees break up the soil.
单选题
Why does land become desert after all trees are cut down?
A
Because nothing remains on land except floods.
B
Because there are no longer trees to keep the rain and protect the top-soil.
C
Because too much rain sinks in and washes away the top-soil.
D
Because roots of the trees break up the soil.
参考解析
解析：
推理题。第三段最后一句指出“When all the top-soil is gone, nothing remains but worthless desert.”表层土壤流失导致了沙漠化，而树木是可以防止水土流失的。
推理题。第三段最后一句指出“When all the top-soil is gone, nothing remains but worthless desert.”表层土壤流失导致了沙漠化，而树木是可以防止水土流失的。
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