单项选择题

Carbon dioxide（）from burning fuels is the most common of the so-called green-house gases.

A. producing
B. having been produced
C. to be produced
D. produced

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单项选择题
—Ring me at 5 am. No, better not so early ! I（）.—I got it.

A. will sleep
B. sleep
C. am sleeping
D. will be sleeping
单项选择题
The old man who（）in the deserted house alone tbr ten years has been settled in a nursing home now.

A. lived
B. had lived
C. has lived
D. has been living
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