What's happening?和What are you doing?

美国人打招呼的What's up,What's happening,How are you doing,What's g what are you doing和what you are doing区别 What's she 还有 what ari you doing?what are they doing?what's what's happening()you?（介词填空） what's happening——you? what's up?what's new,how are you doing?的区别和分别得回答 what are you doing. what you are doing what are you doing What are you doing? What's happening there What happening with you?