may 表示请求,可以时,肯定回答用:Yes,...may.\ Yes,please.\Certainly\ Sure...
否定回答用:No,...can't.\ I'm sorry ...can't.\ I'm afraid...can't.
因为may表示请求别人允许做某件事,回答要用可以、不可以。
所以可以回答为:Yes, you may.\Yes,please.\Certainly\ Sure.
No, you can't. \I'm sorry you can't.\ I'm afraid you can't.
固定用法,你可以背下来。