They had read 3 books by the end of the week.
- общий вопрос
Had they read 3 books by the end of the week?
- вопрос к подлежащему
Who had read 3 books by the end of the week?
- специальный вопрос
What had they read by the end of the week?
- разделительный вопрос
They had read 3 books by the end of the week, hadn't they?
- альтернативный вопрос
Had they read 3 or 4 books by the end of the week?