Употребите must/mustn`t.
7. We wear a uniform.
8. We be late.
9. We listen to the teacher.
10. We do our homework.
11. We drop litter in the class.
12. We pick the flowers from the garden.
13. We keep off the grass.
14. We keep your dog on a lead.
15. We make our bed.
16. We put out the fire.
8 mustn’t
9 must
10 must
11 mustn’t
12 mustn’t
13 must
14 must
15 must
16 must