Question

9. Every possible means to prevent the air pol- lution,but the sky is still not clear.

   A. is used        B. are used

   C. has been used   D. have been used

Answer 1

9. C

9. C解析：句意：为了防止空气污染，每 种可能的办法都试过了，但是天空还是不晴朗。means意为“办法，方法”，单复 数同形，因为此处有every修饰，故应看 作单数;由句意可知，此处应用现在完成 时的被动语态，故选C项。