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