Every possible means to prevent the air pollution but the sky is still not clear.A. has

问题补充：

Every possible means to prevent the air pollution, but the sky is still not clear.

A. has been used

B. have been used

C. is used

D. are used

答案：

(答案→)A. has been used

B. have been used

C. is used

D. are used

解析：句意：每种可能的方式都被使用过来阻止空气污染，但是天空还是不清楚。Means是单复数同形的单词，因为这里被every修饰，所以means这里是单数，谓语用单数，排除BD，从but the sky is still not clear.可知这里强调的是已经被使用了，用现在完成时，选A.