Rabbits can’t / must fly.
can’t
You could / mustn’t forget your book. You’ll need it.
mustn’t
Last year I must / had to learn Chinese. It was really difficult.
had to
I’ve been learning English for seven years, so I can / have to speak it quite well now.
can
You should / mustn’t try harder in class.
should
My mum can’t / couldn’t swim when she was a child.
couldn’t
You mustn’t / don’t have to wash your hair every day. Twice a week is enough.
don’t have to
We had to / could see the sea from the house where we stayed last summer.
could
I have to / can’t study tonight because we have an important test tomorrow.
have to
You can / shouldn’t swim in the lake. It’s very dangerous.
shouldn’t
My grandad mustn’t / didn’t have to study Science at school.
didn’t have to
