听力原文：M: Do you know what happened to me today? I was so embarrassed. W: What? M: Well, Dr Browns class finished ten minutes early, so I went to the library between classes. I knew I didnt have much time, but I wanted to get those books on the Industrial Revolution. I looked them up in the card catalogue and went right to the stacks and found them. So I put them in my book bag and headed back toward the door. Then it happened. The exit gate in front of the door wouldnt open, and a guard immediately warned me that I hadnt checked out my books. He thought I was trying to steal them. W: That must have been embarrassing. But why didnt the exit gate open? M: I asked them that. It seems the books in the library are all magnetically coded, and when you check them out, the librarian behind the desk demagnetises them, then the exit gate will open. W: How interesting! I still dont quite understand how they do it, though. Ill have to go to the library and see it for myself. Questions 13 to 15 are based on the conversation you have just heard. 13. Why did the man decide to go to the library? 14. According to the man, what happens to all the books in the library? 15. According to the man, what does the librarian behind the desk do?13．