answer: #Person2# suggests going to Wangfujing by subway and tells #Person1# there's no additional fare for changing trains.
documents: #Person1#: Let's go to Wangfujing by bus.
  #Person2#: Better take the subway. It's faster, and more convenient.
  #Person1#: En, where do we pay the fares?
  #Person2#: Just go to the ticket office in the subway.
  #Person1#: Do I have to pay an additional fare to change trains?
  #Person2#: No, you don't have to. Here comes the train. Be careful! Subway doors open and close automatically.