Underline the correct modal verbs:
1) Scientists don't have to/must consider the dangers of cloning.
2) People mustn't/don't have to be experts to operate a DVD player.
3) You must/mustn't switch off your computer when it is not in use.
4) She has to/mustn't be 20 years old now.
5) You have to/mustn't be careful with electricity.
6) People don't have to/mustn't take computer lessons to use a computer.
7) John mustn't/has to study hard if he wants to become a robotics engineer.