7. A house is being built, isn't it?
8. A lot of homework is being done by students.
9. Can the letter be torn by Mary?
10. Is this lesson understood?
11. Our children were looked after when we were out.
12. This room hasn't been used for ages.
13. The dog was hit in the garden by the boy yesterday.
14. By whom was this book written?
15. By whom has this room been cleaned?
16. Considerable damage has been caused by the fire.
17. Several new proposals are being considered by the committee.
18. This letter may not be opened, may it?
