In the passive voice, the noun that would be the object of an active sentence appears as the subject of a sentence with passive voice, so, the action described by the verb is being done to the subject by an agent.

Examples:

1. John read the book in one week. (active)

    The book was read by John in one week. (passive)

2. Mike buys a car. (active)

    A car is bought by Mike. (passive)

 

commented

Thank you....very useful

commented

Thanks a lot for your class

commented

if the subject is "somebody" then usually there is no "by ...".  Somebody/something shut the door with a bang>>The door was shut with a bang.    Someone/the enemy destroyed the gate. >> After the gate was destroyed, the defenders surredered.
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