A、Because she needs notice him when the book is available. B、Because it is the registration requirement of the library. C、Becaus

M: Excuse me, I’d like to borrow several books but I don’t know how to find them in the computer index.
W: May I know the titles of the books?
M: Yes, The Sound and the Fury by William Faulkner and The Old Man and the Sea by Ernest Hemingway.
W: Just a second. I’ll see if I can find them for you. (19)The Sound and the Fury is on loan. It’s due back in about one week. I can reserve it for you if you really want it seriously.
M: You mean to say that when it’s returned I shall have the privilege to have it first?
W: That’s right
M: Do you need my address or phone number?
W:(20)You just put your name and address on the front of this card and the name of that book on the back. We’ll drop the book in the mail-box and post it to you when it comes in.
M: That’s a good idea.(21)And what about The Old Man and the Sea?
W:(21)I am so sorry it is on reserve now.
M: So I can’t take it out of the library?
W: No, you can’t.
M: Can I borrow a novel called Babbit by Sinclair Lewis?
W: Yes, you can. But don’t forget to return it by the due date. It is due one month from today.
M: What if I’m not finished with it in a month?
W: You can come in and renew it unless someone else has reserved it.
M: What if I fail to come and renew it?
W: Then you’ll have to pay fines.
M: Thank you very much for your help.
19. Why can’t the man borrow The Sound and the Fury?
20. Why does the woman ask the man to write down his name and address?
21. What do we learn about The Old Man and the Sea?