问题
选择题
Every possible means _______to prevent the air pollution, but the sky is still not clear.
A．are being used
B．have been used
C．has been used
D．had 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．are being used
B．have been used
C．has been used
D．had been used
答案：C