(单选题) Trees are useful to man mainly in three ways,the most important of which is that they can ( )(本题1.5分)

A、 keep him from the hot sunshine
B、 enable him to build warships
C、 make him draw quick profit from them
D、 protect him from droughts and floods
出自:黑龙江省教育学院口语(专升本)

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