Ответ:

1 a. You have to be quiet in exams.

b. You don't have to be quiet at break time.

2 a. I have to do English homework every evening.

b. She has to tidy her room every evening.

3 a. My sister has to go shopping with my parents on Saturdays.

b. My sister doesn't have to go shopping alone on Saturdays.

4 a. We have to do Maths tests every week.

b. We don't have to go to school in the holidays.