A、Colleagues. B、Tutor and student C、Classmates. D、Father and son. C根据上下文推测，此题答案为C

Hu: Hi, John!
John: G’day, Hu! How’s it going?
Hu: All right! But I’m having a bit of trouble finding some of the stuff I need.
John: Really! What’re you looking for?
Hu: Well, I’m just trying to find out a bit about the use of steel in building construction. Have you any ideas?
John: Yeah! Well, speaking offhand, that should be straightforward enough. What about the library? There’s a database on computer, and most of the stuff you need is catalogued—you should be able to find it somewhere or other.
Hu: Yes—but that’s the easy part! You then have to find the book you want on the shelves, and you often find that it’ s out already.
John: I know what you mean! Then you have to line up to borrow it, if it’s CTL.
Hu: CTL? What’s CTL?
John: It means "confined to library": you know—it means you can’t take it out. You have to read it in the library.
Hu: It seems easy, doesn’t it; but you have to reserve it, and then you may want to photocopy bits of it, or make notes — and there never seems to be enough time!
John: Hmm! In your shoes, I think I’d have a word with your tutor.
Hu: I think I’ll do that! Thanks! See you later, Bye!
John: See yah! And good luck!