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
Why was it possible for these ancient trees let more light through than modern ones
A．Because they were closely spaced, only 3 to 16 feet apart.
B．Because they were smaller plants and shrubs.
C．Because their branches did not fan out as far as to form a shape like umbrella.
D．Because they had very small leaves like that of fern and dropped easily.
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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