Identify the correct passive form: 'I heard her sing.'

Perception verb-এর পরে active voice-এ bare infinitive থাকলে passive-এ সাধারণত ‘to + verb’ হয়। তাই ‘I heard her sing’ → ‘She was heard to sing by me’; একইভাবে ‘They saw him enter’ → ‘He was seen to enter.’