happened to do和‘happen to do ;区别?

happened to do和‘happen to do ;区别? happen to do和happen to be doing 的区别? happened to和to happen to的区别 sb happened/happen to do这两个那个对 用happen to do和happen to sb.造句 happen to do和happen to be doing happen to do sth do you know what happened to her,do you know what she happen happen to do or happen doing? 4,happen to do sth Do you happen to know____? Do you happen to know ( )?