单项选择题

What possibly resulted in the evolution from leafless tree to flat leaves

A．The decrease CO₂ in levels.
B．The increase of forests.
C．The drop of temperatures.
D．The change of climates like today.

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单项选择题

According to the fossil reconstruction, what main parts did a tree comprise

A．It comprised a trunk, vertical ridges and palms.
B．It comprised leaves, ferns and palms.
C．It comprised stumps, branches and palms.
D．It comprised a base, a trunk and a crown.

单项选择题

What can people know from the crown of an ancient tree found in New York

A．It helps people know that ancient trees have no trunk.
B．It provides us new information about the appearance of the earliest forest.
C．It provides evidence for the existence of trees 397 million years ago.
D．It provides evidence for the bloom of trees 397 million years ago.

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