Exercise 15. Choose the correct alternative. If you think both alternatives are correct, choose both.

Exercise 15 1. You **must/have to** learn to play an instrument if you want to be a professional musician. (Both are correct: 'must' implies internal necessity/rule for the goal, 'have to' implies external necessity). 2. Builders **don't have to** work in an office. (It is not necessary for them to work there). 3. Doctors **mustn't** tell secrets about their patients' health. (It is prohibited to tell them). 4. **Do you have to** wear a uniform in your job? ('Must you' is very formal and less common in questions). 5. People who work in banks **must/have to** do a lot of paperwork. (Both are correct: 'must' for strong obligation, 'have to' for general necessity). 6. A firefighter **has to/must** work in a team. (Both are correct). 7. An architect **doesn't have to** be fit to do his or her job. (It is not necessary, whereas 'mustn't' would mean they are forbidden to be fit, which is wrong). 8. My sister **has to deal** with the public in her job. ('Must deal' is less common for simple obligation). Exercise 16 2. Builders **must wear hard hats here.** 3. Mark **should work in the summer.** 4. (Based on context: In our school, teachers are not allowed to wear jeans) Teachers **mustn't wear jeans.**