While the pupils were doing classwork,their teacher returned.这个句子都没有知道时间,那为什麼要用Past continue tense呢?
While the pupils were doing classwork,their teacher returned.
这个句子都没有时间暗示,那为什麼要用Past continue tense呢?
这里是属于时间状语从句中的过去进行时,当小学生们当时正在做功课的时候,老师返回来了。
while/when/as 引导的时间状语从句如果是长时间动词,主句是短时间动词,长时间动作用过去进行时,短动作用一般过去时。
While /When /As she was walking on the street, it began to rain.
还有这样的句子,
I was cooking when someone knocked at the door.