5. Sheldon was writing his essay when the power [пропуск].

Sheldon was writing his essay when the power went out.

Продолжавшееся действие дано в Past Continuous (was writing), а внезапное завершённое событие — в Past Simple (went out).

Перевод: Шелдон писал сочинение, когда отключилось электричество.