Every possibles means （）to prevent the air pollution,but the sky_英语解答

Every possibles 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
哪一个?为什么?

人气：223 ℃　时间：2020-05-13 06:57:38

解答

C
从句意看出是已经用过了,所以用完成时；因为前面是every,而means 单复同型,这里是单数,所以选C