1. My father waters this flower every morning.

->This flower is watered by my father every morning. ( S + am/is/are + P2 + by O )

2. John invited Fiona to his birthday party last night.

-> Fiona was invited to John's birthday party by him last night ( S + was/were + P2 + by O)

3. Her mother is preparing the dinner in the kitchen.

->  The dinner is being prepared in the kitchen by her mother ( S + am/is/are + being + P2 + by O )

4. We should clean our teeth twice a day.

-> Our teeth should be cleaned twice a day (  Should + be + V3/V-ed.)

5. Our teachers have explained the English grammar.

-> The English grammar has been explained by our teachers ( S + have/has + been + P2 + by O )

6. Some drunk drivers caused the accident in this city.

-> The accident in this city was caused by some drunk drivers  ( S + was/were + P2 + by O )

7. Tom will visit his parents next month.

-> Tom's parents will be visited by him next month ( S + will + be + P2 + by O )

8. The manager didn’t phone the secretary this morning.

-> The secretary wasn't phoned by the manager this morning ( S + was/were+ not + P2 + by O)

9. Did Mary buy this beautiful dress? 

-> Was this beautiful dress bought by Mary? (Did + S + V-infi + O…? =>Was/were + S’ + Ved/P2 + by + …? )

10. I won’t hang these old pictures in the living room.

-> These old pictures won't be hung in the living room ( S + won't + be + P2 + by O )