1. Someone stole my car last week.
My car was stolen by someone last week.
2. I didn'n feed pigs this morning.
Pigs weren't fed by me this morning.
3. She washes the clothes once a day.
The clothes are washed by her once a day. 
4. Nobody invited her to the party.
She wasn't invited to the party.
5. Dangerous driving causes many accidents.
Many accidents are caused by dangerous driving.
6. My father is repairing the motorbike.
The motorbike is being repaired by my father.