3.
You must be quiet.
You mustn't eat or drink.
You must be careful with the books.
You mustn't leave books on the table when you leave.
You must put the books back in the right place.
4.
1.A
2.B
3.A
4.C
5.B
5.
She mustn't
They can't
You needn't
I don't have to
He doesn't need to