Every possible means _____ to prevent the air pollution, but the sky is still not clear.
Every possible means _____ to prevent the air pollution, but the sky is still not clear.
A、is used
B、are used
C、has been used
D、have been 'used
【正确答案】：C
【题目解析】：means 是一个单复数同形的词.Every means 每一个方法,所以用单数.而且是已经被尝试.所以用被动.

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