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（）