1. It's cold. You should/shouldn't turn on the fan. 2. You ought not to/ought to do homework before you go out with your friends.  3. You should/shouldn't eat plenty of fruit or vegetables every day in order to keep healthy. 4. You must/mustn't eat in the class. 5. You ought to/ought not to drink a lot of water every day. 6. I must/have to submit my homework before 12 o'clock because the deadline is 12 o'clock. 7. I must/have to stay at home to take care of my children. 8. My friend says: "You don't have to/mustn't drink champagne. You can have a coke or fruit juice instead.  9. You don't have to/mustn't drink if you're going to drive afterwards.  10. You don't have to/mustn't pick up Tom at the airport because Judy will