问题
选择题
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
答案
答案：C
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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
答案：C