单项选择题

The greenhouse effect ______.

A．is a problem raised recently
B．has drawn extensive attention all over the world
C．is the warming caused by an increase of CO2
D．should be imputed to the well-developed countries
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单项选择题
The author writes the passage to tell the reader ______.
A．what is the greenhouse effect
B．how serious the greenhouse effect would be
C．it is important to reduce the use of fossil fuels
D．how to change the greenhouse effect
单项选择题
The concentration of carbon dioxide is caused by ______.
A．the heat accumulated in the atmosphere
B．the burning of coal
C．the wide use of renewable energy
D．the destruction of the tropical rain forest
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