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单选题
While _____ an efficiency test on an engine, certain precautions should be observed.
A
making
B
to make
C
being made
D
made
参考答案
参考解析
解析：
句意：在进行发动机的效率测试时要采取一些预防措施。while引导从句时,如主从句的主语一致，且从句谓语又含有be，则从句主语和be可省略。while后可直接跟现在分词、名词、形容词或介词短语。在本题中从句和主句的主语都是人，从句省略了people/workers are。
句意：在进行发动机的效率测试时要采取一些预防措施。while引导从句时,如主从句的主语一致，且从句谓语又含有be，则从句主语和be可省略。while后可直接跟现在分词、名词、形容词或介词短语。在本题中从句和主句的主语都是人，从句省略了people/workers are。
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