what happened 为什么不可以用 what did happen

what happened 为什么不可以用 what did happen 为什么是What happened?而不是 What did happen? what happening?如果错了,解释以下what happened?为什么不能改为what did happen what happened 和what did happen的区别 what happened/what was happened/what is happened/what happen 为什么：他发生了什么?是what happened to him 而不是what did he happen?那为什么又 What happened?中的happen不是动词吗?怎么不是写成What did happen? what happened to him yesterday.为什么要用happened?happen可以吗 What happened to you与how did it happen?的用法 What to him last week?A.did happen B.is happing C.happened D what happened to your car 为什么不用did he walk over to see what happened...什么时候用what is happen 什么时候