题目内容
17.Every possible means _______to prevent the air pollution,but the sky is still not clear.( )A. | are being used | B. | have been used | C. | had been used | D. | has been used |
分析 每一种方法都用了来阻止空气的污染,但是填空仍然不干净.
解答 答案是D.考查被动语态,means当名词解释为"方法",单复数同型,这里有every,说明这里的means为单数,means与动词use之间是被动关系,根据语境所有的方法都用了,应该用完成时,所以答案选D.
点评 被动语态由"助动词be+及物动词的过去分词"构成.被动语态的时态变化只改变be的形式,过去分词部分不变.疑问式和否定式的变化也如此.掌握各种时态的被动语态是解题的关键.
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