1.My father waters this flower every morning.

=> this flower is watered by my father every morning

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

=> Fiona was invited to John's birthday party last night

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

=> The dinner is being prepared in the kitchen by her mother

4.We should clean our teeth twice a day.

=>Our teeth should be cleaned twice a day

5.Our teachers have explained the English grammar.

The english grammar has been explained by our teachers

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

=> The accident was caused by some drunk drivers in this city