Choose the correct options to complete the rules

We use [passive|active] voice when the object is more important than who does the action.

Examples:

Several peoplewere injuredin the accident.

Iwas bittenby a dog when I was a child.

We use passive voice when we [don't know|know] who does the action.

Examples:

My keyswere stolenyesterday.

This churchwas builtin the 19th century.

We use passive voice when we [can|can't] understand who does the action from the context.

Examples:

The criminalswill be arrestedsoon. (by the police)

How oftenisyour carrepaired? (by the mechanic)

We use by to add the [major|agent] to a passive voice sentence.

Examples:

The telephone was inventedbyAlexander Bell.

The letters have been writtenbymy friend.

We don't include the doer (agent) when:

1. The person who performs the action
   [is|isn't] important.

   Example: Three million cars are exported every year.

2. The doer (agent)
   [is|isn't] obvious or already known.

   Example: English is spoken in the UK.

3. The doer (agent)
   [is|isn't] known.

   Example: The car was scratched when it was in the car park.