A、If a student has written a note in it. B、If it was purchased at another store. C、If a professor decides to use another text. D

M: How much would these books cost?
W: (14) That comes to $160.
M: A hundred and sixty dollars! I just can’t believe how expensive textbooks are. (13) And that’s just for required texts.（男士询问这些书的价格，后来又说这些书都是必须的教科书。）Why, if I had to buy all the books on my suggested reading lists, I’d have to take out a bank loan!
W: You could save some money if you bought used texts, you know.
M: I suppose, but it’s hard for me to study from a text that’s been marked up. Tell me, if I don’t need some of these books, can I get a full refund?
W: Sure, if the professor changes his mind about a book or if you drop a course, just return it and we’ll give you your money back — but only for the first three weeks of class. So don’t write your name in the textbook or mark it up until you’re sure you’re going to keep it all semester.
M: And what about at the end of the semester? What’s your buy-back policy?
W: As long as the books are in reasonably good condition, and they’re going to be used in class the next semester, (14) we’ll give you 50 percent of their original value（男士买书一共花了160 美元。学期末男士把书卖给书店的话，书店会给他书的原价的50%，160 美元的50% 是80 美元。）－ even if you didn’t buy them at this store. Of course, (15) if a professor changes texts or if a new edition comes out, we won’t buy them back at all.（如果教授换了教科书或者新出版的一本书，他们就不会回收。）
M: Fifty percent － that’s all?
W: Well. I suppose that doesn’t sound like much, but that’s the store policy.
Questions 13 to 15 are based on the conversation you have just heard.
13. What is the man buying?
14. If the man sells all the books that he buys today back to the store at the end of the semester, how much money will he receive?
15. Why would the bookstore not buy back the man’s books at any price?