When teacher came in,students were reading the book.当老师进来的时候,学生正在读书.
When i opened the door,the telephone was ringing.但我开门的时候,电话响了.
when Tom knocked the door,i was cooking in the kitchen.当汤姆敲门的时候,我正在厨房做饭.
Susan was drinking when her parents got home.当她她的父母到家的时候,苏珊正在喝酒.
Vicky was taking shower when her kitchen caught fire.当薇琪的厨房着火的时候,她正在洗澡.
when后面的从句里不能用过去进行时,过去进行时只能用在后面的主句里.
希望可以对你有用~