While he was working,she _____.A\sleep.B\was sleeping C\sleeping D\slept .为什么答案是B,D不何不行呢

Question

While he was working,she _____.A\sleep.B\was sleeping C\sleeping D\slept .
为什么答案是B,D不何不行呢

Answer 1

while表示两个动作同时进行,while后面的动词一定是延续性动词,主句的谓语动词就不一定了.如果主句的谓语动词也是延续性动词,则主句和从句的谓语动词都必须用doing的形式；如果主句的谓语动词是短暂性动词,则只能用一般过去时的形式.如：
While the students were reading,the teacher came in.
注意：如果短暂性动词作时间状语,只能用when引导.如：
When the teacher came in,the students were reading.
这一题如果she后面是一个短暂性动词,就可以选D.