21. Beer shouldn't be drunk by children.

22. Cars mustn't be parked here.

23. The students' homework have to be done at home.

24. Coffee used to be drunk by my mother when she was young.

25. Flowers oughtn't to be picked up in the school garden.

26. The air may be polluted by burning garbage.

27. That door must be kept closed. 

28. Can this problem be understood by a child?
29. The engine of the car has to be repaired.

30. My hat used to be pulled over my eyes by her.

31. This problem can't be solved by the boys.

32. My Cole used to be visited by John at weekend.

33. Beer shouldn't be drunk by children.

34. Water might be found on the moon.

35. Does this work have to be finished by Tuan today?

=>
21. Beer shouldn't be drunk by children.
22. Cars mustn't be parked here.
23. The students' homework has to be done at home.
24. Coffee used to be drunk by my mother when she was young.
25. Flowers in the school garden ought not to be picked up.
26. The air may be polluted by burning garbage.
27. That door must be kept closed.
28. Can this problem be understood by a child?
29. The engine of the car has to be repaired.
30. My hat used to be pulled over my eyes.
31. This problem can't be solved by the boys.
32. My Cole used to be visited by John at weekend.

33. Beer shouldn't be drunk by children.
34. Water might be found on the moon.
35. Does this work have to be finished by Tuan today?