单项选择题

Experts used to believe that the chief reason for global wanning is _________.

A．that most fuel is consumed in the northern hemisphere
B．human activities
C．natural influences and carbon dioxide
D．the solar energy
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单项选择题
If the assumption about the delay of a new Ice Age is correct _________.
A．the increased levels of carbon dioxide will warm up the earth even more quickly
B．the greenhouse effect will work to the advantage of the earth
C．the best way to overcome the cooling effect will be to burn more fuels
D．ice will soon cover the northern hemisphere
单项选择题
In spite of the greater consumption of fuel in the northern hemisphere, temperatures seem to be falling. This is _________.
A．possibly because of the melting of the ice caps in the poles
B．mainly because the levels of carbon dioxide are rising
C．partly due to the variations of the output of solar energy
D．because the sun presents its "colder" face to the earth
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