All employees are required to ensure that the computers are turned off before______the office.

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问题 All employees are required to ensure that the computers are turned off before______the office.

选项 A、leaving
B、has left
C、to leave
D、leave

答案A

解析 语法:动名词1.before可作为介词,连词使用。2.before做连词时,后面应接完整的句子,(B)选项和(D)选项没有主语,因此排除。3.before做介词时,后不能接不定式,因此(C)选项排除.动名词(A)为正确选项。
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