单项选择题

People have different opinions about ______.

A．why the concentration of gas is rising steadily
B．to what degree the greenhouse effect can affect us
C．whether CO2 has anything to do with the greenhouse effect
D．what measures should be taken to lower the carbon dioxide levels
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单项选择题
What will be the result of the greenhouse effect
A．The earth's temperature will change irregularly.
B．The amount of carbon dioxide will be reduced.
C．The global temperature will gradually increase.
D．Much more sunlight will be blocked by CO2.
单项选择题
What is the specific feature of fossil fuels
A．They are colorless.
B．They are odorless.
C．They are rich in carbon.
D．They are easy to freeze.
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