Passive sentences are used to focus on the object, or when the agent is unknown. The object of the active verb is the subject of the passive verb. Compare:
Active: The boy broke the cup.
Passive: The cup was broken (by the boy).
In passives, the subject does not perform the action in the sentence - the action is performed on it.
The passive is formed by using the auxiliary verb be + past participle.
We use passives more in written English more than spoken English. In passive sentences the agent (the person/thing) that did an action does not have to be mentioned. We use the passive when leaving out the agent, i.e. when the agent is clear, not known or not important.
Decide if these sentences need the active or passive form: