Question

when后为什么加动词ing

Answer 1

因为when后面不是句子（没有主语），所以这时候是当作介词用的，后面的动词就只能用动名词形式，也就是加ing。带连词when的分词短语作状语，如果与主语是主动关系就用现在分词；如果是被动关系就用过去分词。

扩展资料

　　1.be doing sth…when…

　　例：He was still smiling when the door opened and his wife came in.

　　他正笑着的时候门突然开了，他妻子走了进来。

　　2.be about to do sth…when…

　　例：We were about to start when it began to rain.

　　我们刚要出发，天就开始下雨了。

　　3.had not done sth…when…/hardly…when…

　　例：He had not fallen asleep when the telephone rang.

　　他刚要入睡电话就响了。

　　4.had just done…when…

　　例：I had just gone to bed after a very hard day when the phone rang. 在劳累了一天之后我刚刚就寝，电话铃就响了。