They found two ruined buildings.
Общий вопрос:
Did they find two ruined buildings?
Специальный вопрос:
What did they find?
Вопрос к подлежащему:
Who found two ruined buildings?
Альтернативный вопрос:
Did they find two or three ruined buildings?
Разделительный вопрос:
They found two ruined buildings, didn't they?
Типы вопросов выберите сами.