answer: Mark tells the reason why he was late after #Person1# promises #Person1# won't be angry.
documents: #Person1#: Mark, you are not telling me the truth. Now why?
  #Person2#: Promise you are not going to be angry?
  #Person1#: Yes, all right. So why? Go on then. Say it. Oh, really, Mark. I promise I'm not going to be angry. Now why were you late?
  #Person2#: I forgot.
  #Person1#: You forgot? You. . .
  #Person2#: Ah, ah, you promised, and remember?