Nobody informed the police that there had been a mistake.

=> The police was not imformed that there had been a mistake.

21.  Where will your company send you next year?
= Where will you be sent by your company next year ?
22. Who looked after the children when you were away?
= Who were the children looked.
23. Look! Someone is feeding the seals.
= Look ! The seals are being fed.
24. Kathy had returned the book to the library.
= The book had been returned to the library by Kathy.
25. By this time tomorrow, the president will have made the announcement.
= By the time tomorrow, the announcement will be had made by the president.
26. The pollution in the city was affecting people’s breathing.
= People's breathing was being affected by the pollution in the city.
27. Mrs Andrews hasn’t signed those papers yet. Has Mr Andrews signed them yet?
= Those papers have not been signed by the Mrs Andrews yet. Have they been signed by the Mr Andrews yet ?
28. Is a student pilot flying that airplane?
= Is that airplane being flown by a student pilot ?

29. Where did they hold the 1988 Olympic Games?
= Where was the 1988 Olympic Games hold ?
30. Do they make those tractors in this country, or do they import them?