单项选择题

From the passage we know that "the greenhouse effect" is an effect in which ______.

A．low temperatures are created by using a house
B．the house is made green in order to keep heat
C．heat is prevented from escaping outside
D．everything is kept green in a house

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单项选择题

Which of the following statements is NOT true

A．It is the production by termites that is now of greater concern.
B．What scientists worry more about is the output from burning fuels.
C．The output from burning fuels is now rising steadily.
D．The burning of fuels generates much less carbon dioxide than termites do.

单项选择题

Which of the following sentences is true

A．Carbon dioxide in the atmosphere carries heat into outer space so as to change the climate.
B．Carbon dioxide may escape into the greenhouse so that the Earth will be made warmer.
C．As carbon dioxide keeps heat from escaping into outer space, the Earth may become warmer.
D．Carbon dioxide may make the Earth warmer because it lets the heat escape into outer spac

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