happen to do

happen to do sth happen to do or happen doing? 4,happen to do sth Do you happen to know____? Do you happen to know ( )? sb.happen to do sth. 用happen to do和happen to sb.造句 happen to do和happen to be doing happen to do和happen to be doing 的区别? sb.happen to do sth.意思辨析 happen to do sth什么意思 happen to do sth的汉语是什么?