answer: #Person2#'s girlfriend wants to learn the butterfly stroke, and #Person1# asks her to follow #Person1#. #Person1# swims just for fun.
documents: #Person1#: Does your girl friend like swimming?
  #Person2#: Yes, she does. She is good at backstroke and free style.
  #Person1#: Then you can help her with the breaststroke and sidestroke.
  #Person2#: But she wants to learn the butterfly stroke
  #Person1#: Really? Then just ask her to follow me.
  #Person2#: I heard you are now practicing underwater swimming, aren't you?
  #Person1#: Yes. But I still have some difficulties it breathing.
  #Person2#: Say, kid, keep on practicing, you're sure to be a first-class swimmer.
  #Person1#: To tell you the truth, I have never thought of being a swimmer. I swim just for fun.
  #Person2#: That's good.