Поставить в страдательный залог: 11. the pupils can do this exercise without any difficulty. 12. you must not leave your bags in the hall. 13. they don't look after the children properly.
11. This exercise can be done by the pupils without any difficulty. 12. Your bags must not be left in the hall. 13. They children aren't properly looked after.
12. Your bags must not be left in the hall.
13. They children aren't properly looked after.