Must/mustn't

You look pale. I think you … see the doctor.

  It’s very slippery outside. You … run there.

 You … throw rubbish on the pavement.

  Children … look neat and clean at school.

You … make noise in the library.

  You … brush your teeth before going to bed.

You … fasten your seatbelt in a car.

Children … watch TV a lot.

 You … light a fire in the forest.

You ... be friendly to other people.