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Why is a "secondary succession" quicker

A．The ground is more suitable.
B．There is more space for new plants.
C．Birds and animals bring new seeds.
D．It is supported by the forest.
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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.

单项选择题What has sometimes caused plants to die out

A．Interference from foresters.
B．Variations in climate.
C．The absence of wooded land.
D．The introduction of new type of plants.