当你做错事向别人表示歉意,你应该说：

答案C
解析：表示道歉的常用语有：Excuse me(for…)／I'm sorry.／I hope you'll excuse me.／I beg your pardon.／I must apologize.等等.应答语有：It doesn't matter(at all).／It's nothing.／Not at all.／That's(quite)all right(OK).／Please don't worry about that.／Never mind about that.／Please think nothing of it.／Let's forget it.／No problem.等等.
拓展延伸：在需要打扰或冒犯对方时,常用Excuse me.当自己有过错需要对方原谅时,可用Excuse me(for…)或I'm sorry…但在某些场合你并没有过错时,要慎用I'm sorry,以免承担不应承担的责任.