单项选择题

According to the passage, ______.

A．a long time ago, man did not know how to make use of wood
B．trees are not as useful as they were in the past
C．trees were more found in the past than they are today
D．people have 'always found trees useful

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热门试题

单项选择题

Some deserts were once ______.

A．very good lands
B．covered by ice
C．very cold
D．dry and useless

单项选择题

From the passage, we know that man must ______.

A．do nothing to keep the balance (平衡)of nature
B．try his best to change the balance of nature
C．try his best to keep the balance of nature
D．do his best to stop the balance of nature