Put these sentences into the passive voice

Giúp mình làm mấy câu này nha:
Đề bài: Put these sentences into the passive voice.
19. When is someone going to announce the results of the contest?
20. Nobody informed the police that there had been a mistake.
21. Where will your company send you next year?
22. Who looked after the children when you were away?
23. Look! Someone is feeding the seals. 2
4. Kathy had returned the book to the library.
25. By this time tomorrow, the president will have made the announcement.
26. The pollution in the city was affecting people’s breathing.
27. Mrs Andrews hasn’t signed those papers yet. Has Mr Andrews signed them yet?
28. Is a student pilot flying that airplane?
29. Where did they hold the 1988 Olympic Games?
30. Do they make those tractors in this country, or do they import them?