问题
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
答案
答案：D
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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
答案：D