单项选择题

What has sometimes caused plants to die out of the past

A．Interference from foresters.
B．Variations in climate.
C．The absence of wooded land.
D．The introduction of new type of plants.
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单项选择题
What conditions are needed lot shrubs to become established
A．Ferns must take root.
B．The ground must be covered with grass.
C．More soil must accumulate.
D．Smaller plants must die out.
单项选择题
The author of the passage does not believe that ______.
A．people can protect themselves
B．the truth makes men free
C．leaders have to be consistent
D．princes are human
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