1. People believe that 13 is an unlucky number.
⇒ 13 is believed to be an unlucky number.
2. They know that English is an international language.
⇒ English is known to be an international language.
3. I have heard her sing this song several times.
⇒ This song has been heard to sing several times by her.
4. People saw him steal your car.
⇒ He was seen to steal your car.
5. They say that John is the brightest student in class.
⇒ It's said that John is the brightest student in class.
6. Open your book. / let your book be opened
⇒ Your book is opened.
7. She advised me to sell that house.
⇒ I was asvised to sell that house by her.
8. It is dangerous for us to take the short cut.
⇒ It is dangerous for the short cut to be taken.
9. They think that he has died a natural death.
⇒ It's thought that he has died a natural death.
10. He won’t let you do that silly thing again.
⇒ You won't be let to do that silly thing again.