题目内容
【题目】If the new safety system _______ to use, the accident would never have happened.
A. had been put B. were put C. should be put D. would be put
【答案】A
【解析】考查虚拟语气。句意:如果这个新的安全系统被投入使用过的话,这个事故就不会发生了。根据主句确定是对过去情况的虚拟,所以从句用had done形式,system与put to use是动宾关系,故选A。
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