Rewrite the sentences using the passive voice

21. The computers are used by the students at their lessons.
22. The rules of the game were explained to the students by the teacher.
23. The office will be cleaned by them tomorrow.
24. The costumes for Cats were designed by John Napier.
25. The dinner is served by them from 7:00 pm onwards. 

21. Computers are used by students at their lessons.22. The rules of the game were explained to the students by the teacher.23. The office will be cleaned tomorrow.24. The costumes for Cats were designed by John Napier.25. Dinner is served from 7:00 pm onwards.