单项选择题

Those studies carried out in North Carolina suggest that _________.

A．trees' function for absorbing carbon dioxide is limited
B．carbon dioxide is the main cause for global warming
C．leaves falling from trees can emit more oxygen
D．more carbon dioxide is beneficial for trees' growth for many decades
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单项选择题
The committee report of National Academy of Sciences in Washington reveal that _________.
A．ice from Antarctica and Greenland is appropriate to show the change
B．carbon dioxide is released mainly from the fuel
C．level of carbon dioxide increases with global temperatures
D．carbon dioxide is helpful for tree growth
单项选择题
Which one is NOT mentioned in this passage that can be the source of carbon dioxide
A．Oil.
B．Trees.
C．Wood.
D．Soil.
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