1. 13 is believed to be an unlucky number.

2. English is known to be an international language.

3. This song has been sung by her several times.

4. He was seen stealing your car.

5. John is said to be the brightest student in the class.

6. Let your book be opened.

7. I was advised to sell that house by her.

8. It is dangerous for the shortcut to be taken by us.

9. He is thought to have died a natural death.

10. You aren't allowed to do that silly thing again.

11. It is ordered that the floor be cleaned.

12. The earth is believed to have stood still.

13. The children aren't made to work hard.

14. That silly thing shouldn't be done again.

15. We are begged to help him.