◎ 题干
Every possible means ________ to prevent the air pollution, but the sky is still not clear.
[     ]
A. has been used
B. are used
C. is used
D. have been used
◎ 答案
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◎ 解析
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◎ 知识点
    根据魔方格专家分析,试题“Every possible means ________ to prevent the air pollution, but the sky is still not clear. [ ]A. has been usedB. are usedC. is usedD. have been used…”主要考查了你对  【现在完成时的被动语态】  等知识点的理解和应用能力。关于这些知识点的“档案”,你可以点击相应的链接进行查看和学习。