作业帮All the apparatus______ before the experiment began.1.have been tested 2.had been tested
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All the apparatus______ before the experiment began.1.have been tested 2.had been tested
All the apparatus______ before the experiment began.1.have been tested 2.had been tested
All the apparatus______ before the experiment began.1.have been tested 2.had been tested
选择2 had been tested
before引导时间状语 表示过去某一时间或动作之前已经发生或完成的动作或存在的状态.
句意：在试验开始前、所有器械已经被检查过了
“检查器械”是发生在“实验开始”前,
began是用的过去式、所以“检查（test）”这个动作要用过去完成时 表示“过去的过去”