听力原文： W: Can I help you？
M: Yes, my son and my daughter bought this pen here for my wife's birthday, but it doesn't work so I'd like to exchange it.
W: I see, do you have the receipt with you？
M: Yes, here it is.
W: OK, let me see the pen please. Hmm. It doesn't work at all, does it？ We'll be happy to exchange it for you. Let's see, I'm afraid we don't have another purple one.
M: Oh, now what will I do？
W: Would you like to choose a different color？ We do have this pen in black and yellow.
M: My wife doesn't care for either of those colors. You don't have any other colors？
W: We have it with a red leather cover. That's three dollars more.
M: I don't think so. The children worked hard to save up the eleven dollars for this one. They would probably be upset if I paid for part of their present.
W: If you want, we can order another pen just like this one. There wouldn't be any extra charge for it.
M: That sounds like a good idea. Thank you.
Why did the man’s children buy the pen？

A. It’s a present for the man’s birthday.
B. It’s a birthday present for the man’s wife.
C. It’s a birthday present for the man’s son.
D. It’s a birthday present for the man’s daughter.