Active voice passive voice
s+v+ob ob+v3+sub
Rule: Any sentence when mentioned in the simple form of a tense, we use an auxiliary from the continuous form of the same tense (was, were, is, am, are, has been, have been) before the verb. Remember we use the past participle form of verbs in passive voice.
Example- Rahul played cricket. (simple past)
Cricket was played by Rahul. (past Conti auxiliary + V3)
Therefore, Columbus discovered America. (Active voice)
America was discovered by Columbus. ( Passive voice)