The correct passive of ‘Sheila was writing a letter’ is-

✅ কেন সঠিক: Past continuous passive = was/were + being + past participle. So: A letter was being written by Sheila.

❌ অন্য অপশন: ক and খ use ‘writing’ instead of the past participle ‘written’; ঘ uses ‘been’ in place of ‘being’.

💡 মনে রাখুন: Continuous tense in the passive always needs ‘being’: is being done, was being done.