怎么区别when+过去进行时还是过去时?

问题描述:

怎么区别when+过去进行时还是过去时?

我是英语老师帮帮你.
when 引导的从句中,如果动词是终止性即瞬间动词,则用过去时,主句用过去进行时.如:What were you doing when I came in?