31 You can't/don't have to enter this room; it's for staff only. 32 I must/can't do something to help the environment but I don't know what. 33 You can't/shouldn't buy any products you don't really need.

31. You can't/don't have to enter this room; it's for staff only.

    Вам нельзя/не нужно входить в эту комнату; она только для персонала.

32. I must/can't do something to help the environment but I don't know what.

    Я должен/не могу сделать что-то, чтобы помочь окружающей среде, но я не знаю что.

33. You can't/shouldn't buy any products you don't really need.

    Вам нельзя/не следует покупать продукты, которые вам действительно не нужны.

Ответ:

1. can't
2. must
3. shouldn't