Ex. 3
1. You mustn't bring food and drink into the lab.
2. You must ask a teacher before you print anything.
3. You mustn't tell others your password.
4. You must turn off your computer when you leave.
5. You must leave the lab before 5 pm.
Ex 4.
1. You must be careful when you use a knife.
2. You mustn't touch the exhibits.
3. I strongly advise you that you must tell him the truth.
4. You mustn't take pictures here; it'a against the rules.
5. We must listen to our teacher.
