单项选择题

In a "primary succession", what makes it possible for mosses to take root

A．The type of rock.
B．The amount of sunlight.
C．The amount of moisture.
D．The effect of lichens.
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单项选择题
What conditions are needed for 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
What does the forest strike mankind as permanent
A．The trees are in community.
B．The forest is renewed each season.
C．Man's life is short in comparison.
D．It is an essential part our lives.
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