对不起 ：
(I am) sorry.
(I am) sorry to trouble you.
Excuse me.
Pardon.
I beg your pardon.
不用谢：
It's my pleasure.
You are welcome.
Don't mention it.
My pleasure.
That's OK.
That's all right.
没关系：
Not at all.
That's all right.
Never mind.
Forget （about） it.
That's OK.
It doesn't matter.