that is ok与not at all在回答“对不起”时的区别?

题目

that is ok与not at all在回答“对不起”时的区别?
例题；
--Professor Johnson,I'm afraid I can't finish the report this day .
--( ).How about next week?
A.Not at all.B.That'OK.

答案

选择 B.That'OK.
原句翻译：Johnson教授,我怕我今天不能完成这个报告
没关系,下礼拜怎么样?
A.Not at all.一点儿也不,针对夸奖 ,多用来回答thanks
B.That'OK.好的,没关系.针对道歉 ,多用来回答sorry