1. They will have finished their work by next week.
⇒ Their work will have been finished by next week.
2. It's said that the fire has caused considerable damage.
⇒ Considerable damage to have been caused by the fire.
⇒ People say that the fire has caused considerable damage.
3. The police wanted the man help them find the suspects.
The police wanted helping the fire has caused considerable damage.
4. We're going to give David a pig surprise.
⇒ David is going to be given a pig surprise (by us).
5. I think Alfred Nobel invented dynamite.
⇒ It's thought that Alfred Nobel invented dynamite.
⇒ Dynamite is thought to have been invented by Alfred Nobel.
6. Your hair is long, you ought to get it cut.
⇒ You ought to get your long hair cut.
7. Keep the secret.
⇒ Let the secret be kept.
8. Don't close your book.
⇒ Let your book not be closed.
9. They made him work all day.
⇒ He was made to work all day.
10. Parents like their children visiting them at weekends
⇒ Parents like being visited by their children at weekends.