用must, mustn't, can, can't填空。

1. Don't open your present now! In China you _____  wait and open it later.

2. —Can I do cleaning at Spring Festival?

    —No, you_____  .  

    —It's bad luck.

3. In America you _____  open your present immediately.

You don't have to wait!

4. In Britain you _____  ride your bicycle on the pavement _____. It's too dangerous.

5. In Britain, you _____ be 18 if you want to drive a car.