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英语选择1We were having a discussion—— our teacher came inA.when

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英语选择1
We were having a discussion—— our teacher came in
A.when B,as C.while D.before
英语选择1We were having a discussion—— our teacher came inA.when
A when
when既可指时间点,也可指一段时间;而while只能指一段时间.当老师进来的时候我们正在讨论.指的是一个时间点所以排除while.
当从句中的谓语动词是持续性的动作时,我们可以用while,when或as.这里不是句首,所以排除as.
至于before,从来没有考虑过吧.如果用before的话,前面应该是过去现在时,而不是过去进行时.所以直接排除掉before.
下面就不用说了吧.