PASSIVE

By Esther Tejado.

The passive voice is the alteration of an active sentence where the complement becomes the subject and the subject becomes the agent. It is used when you don’t know who does the action, and also to focus the attention in the person who experiences the action. The passive voice is made with the integration of the verb to be (in the same time that in the active sentence) followed by the main verb in past participle. Ex: The Mona Lisa was painted by Leonardo Da Vinci.                                                                                                                                  
 *when the subject is clear, the sentence has not agent. Ex: he hasn’t done the laundry yet - the laundry hasn’t been done yet.
*when the agent is an instrument it is used the preposition "with". Ex: he was hurt with a knife.
*verbs without object cannot be passive (intransitives).

Active	Passive
Present simple: clean	Is/are cleaned
Present continuous: is/are cooking	Is/are being cooked
Past simple: cut	Was/were cut
Past continuous: was/were reading	Was/were being read
Present perfect: has/have filmed	Has/have been filmed
Past prefect: had won	Had been won
Future simple: will eat	Will be eaten
Future continuous: will be cleaning	Will be being cleaned
Future perfect: will have done	Will have been done

Verbs such believe, claim, consider, know, say, think and understand are often used in passive followed by the present infinitive. This structure is common in journalism.

Ex: she is believed to be suffered from heart disease. 

Reference: Straightforward for Advanced, second edition.
 https://www.ef.com/english-resources/english-grammar/passive-voice/