6. We heard the sound of music.
=>The sound of the music was heard by us
7. The police arrested ten men
=>Ten men was arrested by the police
8. She didn’t send that letter yesterday.
=>That letter wasn't sent by her yesterday
9. Columbus discovered America in 1492.
=>America was discovered by Columbus in 1492
10. The doctors ordered him to take a long rest.
=>He was ordered to take a long rest by the doctor