---Peter ,please be quick.I "ll be late for the party.

问题描述:

---Peter ,please be quick.I "ll be late for the party.
---People ____ fasten the seat belt or they"ll be fined.You must do it first.
A.may B.can C.dare D.must
请详解.

D 涉及生命问题必须用must加强语气