题目内容
Every possible means ________ to prevent the air pollution, but the sky is still not clear.
[ ]
A.are being used
B.have been used
C.has been used
D.had been used
答案:C
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题目内容
Every possible means ________ to prevent the air pollution, but the sky is still not clear.
A.are being used
B.have been used
C.has been used
D.had been used