answer: #Person1# tells #Person2# David broke his leg because of the horse frightened by a dog. #Person2# thinks riding a horse and driving are dangerous.
documents: #Person1#: I came across David in the hospital this morning. He broke his left leg when he was learning to ride a horse earlier this morning.
  #Person2#: What happened exactly?
  #Person1#: The horse is frightened by a dog and started running fast. David lost his balance and fell to the ground.
  #Person2#: That's dangerous. I'd never try that.
  #Person1#: You are too timid. You don't even want to learn how to drive.
  #Person2#: That's dangerous, too. Besides, I don't need to learn how to drive. You are a good driver, aren't you, honey?
  #Person1#: But I cannot take you everywhere you want to go.
  #Person2#: I seldom go out.