紧急...I was cooking a meal when you _____at the door. A. knocked B. were knocking

当一个动作发生的时候（过去时），另一个动作正在进行（过去进行时），故用A knocked ，另外，while后面的动词一般是持续性动词，如：My mother was cooking while my father was reading.

A
when表示正在这时

A

A

A