Turning the active into the passive.
Remember some rules if you want to change the active into the passive.

1. The object becomes the subject in the passive sentence.

She prints documents. (Active)
The documents are printed. (Passive)

2. The active verb changes into the passive form.

We plant trees every year. (Active)
The trees are planted every year. (Passive)
3. The subject of the active sentence becomes the agent.

Sarah baked a cake. (Active)
The cake is baked by Sarah. (Passive)
4. Object pronouns becomes subject pronouns.
He sent this letter to me. (Active)
I was sent this letter. (Passive)
5. When the subject is one of these words: one, someone, they, he, people etc., the agent is often omitted in the passive sentence.
People often buy presents on Christmas Day. (Active)
The presents are bought on Christmas Day. (Passive)
6. Only the verbs that take an object can be turned into the passive.

Kim is cleaning the room now.  (Active)
The room is being cleaned by Kim now. (Passive)

It is raining today. (It is impossible to change this sentence into the passive because the verb has no object)