Question

: The computer class starts at 7:00.
: We don't have to/mustn't be late.
Are you on a diet?
Yes, the dietician says I must/have to eat lots of fruit.
You mustn't/don't need to buy tickets. Entrance is free.
Really?
You shouldn't/mustn't enter this room.
I'm sorry. I didn't see the sign, sir.​

Answer 1

1. musn't

2. have to

3. don't

4. musn't