What was he doing his father back?A. while; came B. when; came C. when; was coming

问题补充：

What was he doing his father back?

A. while; came B. when; came C. when; was coming

答案：

解析：句意:当他的父亲回来的时候，他正在做什么？while当……时候，后跟的动词通常是持续性动词；when当……时候，后跟的动词通常是持续性动词或非持续性动词；因为在主句里的动作发生在过去，所以从句的动作也是发生在过去。根据句意故选B。