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    All these 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 【查看更多】

     

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    All these 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

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    All these 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

     

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