1. People balive 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.

→ Your book is opened

7. She asvised me to sell that house.

→ I was asvised to sell that house by her

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