M: It’s Julia’s birthday tomorrow.
W: Are you sure I think it should be the day after tomorrow.
M: Well, let me see. Oh, I’m sorry. You’re right. It is the day after to- morrow. Shall we buy her a gift
W: Yes, of course. Shall we get her a new pen
M: That sounds good. But I think it’s better to buy her a box of chocolates.
W: Julia doesn’t like sweet things. Didn’t you know that
M: You’re right. Er... I know. We can give her a record, for she loves music very much.
W: That’s great. Let’s go to the music shop now.

Why has the captain asked the passengers to keep their seat belts on（）

A. The plane is going to land.
B. The plane is going to take off.
C. The air might become very rough.