The key answer of exercise 4

a)

1. have to
2. don't have to
3. has to
4. don't have to
5. have to
6. don't have to
7. doesn't have to

b)

1. Men have to / don't have to join the army.
2. Women have to / don't have to join the army.
3. A new driver has to / doesn’t have to take a driving test.
4. People have to / don't have to go to school when they are 17.
5. Schoolchildren have to / don't have to study English.
6. You have to / don't have to have a passport to leave the country.
7. There has to / doesn’t have to be an election every year.