Correct Answer & Explanation
Option B
• This sentence describes an action that was in progress in the past when another past action occurred.
• 'When I entered the room' indicates a specific point in the past.
• The action 'singing' was ongoing at that specific past moment.
• This scenario requires the Past Continuous Tense.
• The structure for Past Continuous Tense is Subject + was/were + V1-ing + Object.
• 'She' is a singular subject, so 'was singing' is the correct form.