1. These exercises were done well.

`→` They did the exercises well.

2. This dress must be washed in cold water.

`→` She must wash this dress in cold water.

3. No mistakes have been made in his composition.

`→` He hasn't made any mistakes in his composition.

4. His painting will be exhibited for the first time by New Arts gallery.

`→` They will exhibit his painting for the first time by New Arts gallery.

5. This house was built 100 years ago.

`→` They built this house 100 years ago.

6. These artificial flowers are made of silk.

`→` They make these artificial from silk.

7. The lessons are being written by the students now.

`→` The students are writing the lessons now.

8. This job has to be done at once.

`→` We have to do this job at once.

9. These animals at the zoo are fed twice a day.

`→` They feed these animals twice a day at the zoo.

10. The operation is going to be performed by French doctors.

`→` French doctors are going to perform the operation.

11. All the arrangements have been made.

`→` They have made all the arrangements.

12. When was this radio manufactured?

`→` When did they manufacture this radio?

13. They couldn't be found anywhere.

`→` We couldn't find them anywhere.

14. Is mathematics taught in this school?

`→` Is she teach mathematics in this school?

15. Fortunately the machinery wasn't damaged by the accident.

`→` The accident didn't damage the machinery fortunately.

16. Please wait here while your luggage is being examined.

`→` Please wait here while we are examining your luggage.

17. How are candles made?

`→` How do they make candles?

18. For a long time the earth was believed to be flat.

`→` For a long time they believed that the earth was flat.

19. Were you taught how to apply this theory by your teacher?

`→` Did your teacher teach you how to apply this theory?

20. Apples are said to be good for our health.

`→` They say that apples are good for our health.

21. Don't let the dog be teased by the children.

`→` Don't let the children tease the dog. 

1. They did the exercises well.

2. She must wash this dress in cold water.

3. He hasn't made any mistakes in his composition.

4. They will exhibit his painting for the first time by New Arts gallery.

5. They built this house 100 years ago.

6. They make these artificial from silk.

7. The students are writing the lessons now.

8. We have to do this job at once.

9. They feed these animals twice a day at the zoo.

10. French doctors are going to perform the operation.

11. They have made all the arrangements.

12. When did they manufacture this radio?

13. We couldn't find them anywhere.

14. Is she teach mathematics in this school?

15. The accident didn't damage the machinery fortunately.

16. Please wait here while we are examining your luggage.

17. How do they make candles?

18. For a long time they believed that the earth was flat.

19. Did your teacher teach you how to apply this theory?

20. They say that apples are good for our health.

21. Don't let the children tease the dog.