What happened to you与how did it happen?的用法

What happened to you与how did it happen?的用法 happen用法what's happened to you What's happened toyou what ha what happen to you还是what happened to you? what happened 和what did happen的区别 请问：happen的用法.eg:what happened,what's happen的区别 What ____ you yesterday A happen B happen to C happened to D ----How did this accident happen?----You know ,it ___ diffic What to him last week?A.did happen B.is happing C.happened D what happened 为什么不可以用 what did happen 为什么是What happened?而不是 What did happen? do you know what happened to her,do you know what she happen What did happen to you the day before yesterday?(改错)