16. They say that John is the brightest student in class

=>it is said that John is the brightest student in class

17.They reported that the President had suffered a heart attack

=>it was reported that the President had suffered a heart attack
 

18.They think that he has died a natural death

=>it is thought that he has died a natural death
 

19.They reported that the troops were coming

=>it was reported that the troops were coming

20.People believed that the earth stood still

=>it was believed that the earth stood still