That joke ... be really funny
need to
mustn't
have to
must
What does she have to do?
She has to / must throw away the milk; She must buy some milk.
He ... practise a lot.
doesn't need to
need to
have to
must
They can swim very well. They ... learn how to swim.
don't have to
doesn't need to
mustn't
need to
He ... work any longer.
don't need to
doesn't need to
needs to
mustn't
What does the baby need to do?
He needs to sleep.
What does he have to do?
He has to / must buy some food; He must go shopping.
What does he have to do?
He has to / must be careful when crossing the street.
What does he need to do?
He needs to learn how to ride a bike / He needs to buy a new bike.