过去进行式 (was/were + V-ing)

过去某一动作发生时(V-ed)正在进行的另一动作(was/were + V-ing)

What were you doing when he came? 他来的时候你在做什么？

I was writing a report when he came. 他来的时候我正在写报告。

What were they doing when the earthquake happened?

地震发生的时候他们在做什么？

They were watching TV when the earthquake happened.

地震发生的时候他们正在看电视。

My mother cut her finger while she was cooking.

我妈妈做菜时切到手指。

I was taking a nap when you called yesterday.

你昨天打电话来的时候我正在午睡。