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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单项选择题
After reading the passage, we may conclude_______.
A．the author is worried about the greenhouse effect
B．the author asks all of us to reduce the use of coal
C．the greenhouse effect is welcome as it is a mixed blessing
D．the greenhouse effect has affected our life now
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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