Select the option that is grammatically correct:

The correct answer is Option (3) → Only when the last guest had eaten did Nani sit down for her own meal.

“Only when” at the start:

• When a sentence starts with “Only when”, “Only after” or “Only then”, the helping verb comes before the subject in the main part.
• Here the main part is did Nani sit down. “Did” comes before “Nani”, and the verb after it is the plain form “sit”. The when-part keeps the normal order: “the last guest had eaten”.

Why the Other Options are Incorrect?

Option 1: Kiran answered confidently every question at the interview. — Incorrect. The option says “answered confidently every question”. An adverb does not come between a verb and its object.
Corrected: Kiran answered every question confidently at the interview.

Option 2: Rohan found his old cricket bat in the store room and gave away it to his cousin. — Incorrect. The option says “gave away it”. With a pronoun object, the pronoun goes between the verb and the small word.
Corrected: Rohan found his old cricket bat in the store room and gave it away to his cousin.

Option 4: Sunil enjoys early-morning walks, and so his wife does. — Incorrect. The option says “so his wife does”. In a short addition, “so” is followed by the helping verb and then the subject.
Corrected: Sunil enjoys early-morning walks, and so does his wife.