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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

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

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

 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