answer: Li calls Bobby to tell him Li can't arrive on time due to a traffic jam. Bobby will put off the dinner till one o'clock
documents: #Person1#: Hello, Bobby , It seems that I can't arrive at your home by 12 o'clock. 
  #Person2#: What happened? We're all expecting you , Hans , Dick , Archie. . . 
  #Person1#: I'm so sorry, I've been held up by the damn traffic jam for half an hour. I'd have arrived but for that. 
  #Person2#: I see. Where are you now, Li? 
  #Person1#: Thirty meters ahead is the Waterloo Bridge. 
  #Person2#: It is not far away from home. It is... Let me see, about 20 minutes' walk. Can you walk here?'
  #Person1#: I've thought of that, but what can I do with my car? If only I had taken a taxi! 
  #Person2#: That's too bad, But don't worry. We'll put off dinner till one o'clock. 
  #Person1#: I'm so terribly sorry to keep you waiting. 
  #Person2#: It doesn't matter. Bye. 
  #Person1#: Bye.