Put in 'mustn't' or 'don't / doesn't have to':
1) we have a lot of work tomorrow. you -be late.
2) you - tell anyone what i just told you. it's a secret.
3) the museum is free. you - pay to get in.
4) children - tell lies. it's very naughty.
5) john's a millionaire. he - go to work.
6) i - do my washing because my mother does it for me.
7) you - smoke inside the school.
8) you can borrow my new dress, but you - get it dirty.
9) we - miss the train, because it's the last one tonight.
10) she - do this work today, because she can do it tomorrow.