1、由when引导的时间状语从句，主句用过去进行时，从句用一般过去时。如：When he was still a little boy,Jack London wrote some compositions which were praised by his teachers.杰克·伦敦还是小孩时，他写的一些作文就受到老师的赞赏。
2、while通常用在事情同时发生的情况，主句和从句都用过去进行时。如：Mother was cooking the meal while i was doing my homework。我做作业时，妈妈正在做饭。
She got married while she was working as a waitress。她在饭店当服务生期间结婚了
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