He opened the door.

1. The door was opened by him.
2. The door is being opened by him.
3. The door is opened by him.
4. The door was being opened by him.

Converting simple past active to passive requires: object (door) becomes subject + was/were + past participle (opened) + agent (by him). Since “door” is singular, “was” is correct. Simple past passive indicates a completed action in the past with focus on the door rather than the opener. This transformation is fundamental in English and appears frequently in narratives when the object is more important.