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.
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