I. Rewrite the following sentences and add the available modal verbs to the appropriate position.

1. If you go swimming in the sea, you wear a life jacket. (ought to)

2. I will tell you my secret, but you tell anyone. (mustn't)

3. You spend too much time playing computer games. You stop that. (must)

4. Phuong loves chocolate, but she eat too much, or she will gain weight. (oughtn't to)

5. We wear helmets when we ride a motorbike. (have to)

6. I book the tickets in advance. (don't have to)

7. Alia, you say rude words like that. (mustn't)

8. We play table tennis. We can play chess instead. (don't have to)

9. Children put their hands into sockets. That is very dangerous. (mustn't)

10. Doctors sometimes work at the weekends and on national holidays. (have to)