Вот примеры вопросов к предложению "The children were singing when Mother returned home":
Общий вопрос: Were the children singing when Mother returned home?
Специальный вопрос: What were the children doing when Mother returned home?
Альтернативный вопрос: Were the children singing or playing when Mother returned home?
Разделительный вопрос: The children were singing when Mother returned home, weren't they?