happen/ 'hæpən /

1.vi.[incident] [ accident+] 
(occur,result) 发生

What's happening?
发生什么事?
what will happen if...?
如果…会怎么样?
tell me what happened
告诉我发生了什么事
to happen to do sth
刚巧做某事
as it happens
碰巧
it's the best thing that ever happened to me
我从未遇上这么好的事情