单项选择题

It can be concluded that a concentration of carbon dioxide in the atmosphere would ______.

A．mean a warming up in the Arctic
B．raise the temperature of the earth's surface
C．prevent the sun's rays from reaching the earth's surface
D．account for great changes in the climate in the northern hemisphere
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单项选择题
On the basis of their models, scientists are of the opinion that ______.
A．the climate of the world should be becoming cooler
B．the new Ice Age will be delayed by the greenhouse effect
C．the man-made warming effect helps to increase the solar effects
D．it will take thousands of years for the inertia of the earth's climate to take effect
单项选择题
Although the fuel consumption is greater in the northern hemisphere, temperatures there seem to be falling. This is ______.
A．mainly because the levels of carbon dioxide are rising
B．partly due to variations in the output of solar energy
C．possibly because the ice caps in the poles are melting
D．exclusively due to the effect of the inertia of the earth's climate
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