完型填空中总是出现的as,when,since,beore,while怎么区分?

题目

完型填空中总是出现的as,when,since,beore,while怎么区分?
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答案

1.首先从词义上分：as表示“当.时候”,when“当.时候”,since表示“自从”,while“当.时候”,before表示“在.之前”根据这一项,可以区分开since和before与其它三项.
2.从细微差别来看,as表示一边一边,when表示这时,while表示对比.
He was doing his homework while she was watching TV.他在做作业的时候,她在看电视.
He was doing his homework as he was listening to music.他边做作业边听音乐.
He was doing his homework when a cat came into his room.他一直在做作业这时有一只猫进入的他的房间.