есть 5 основных типов:
Tom is reading a book now.
1. общий
Is he reading a book now?
2. альтернативный
Is Tom reading a book or a newspeper?
3. с хвостиком
Tom is reading a book now? isn't he?
4. к подлежащему
Who reading a book now? или who reads a book?
5. специальный со словами when where why итд
What is Tom doing now?
where is he reading a book?