My friends discussed their plan in detail.
My friends didn't discuss their plan in detail. Не обсуждали план подробною
Did my friends discuss their plan in detail? Общ. вопрос.
Did my fiends discuss their plan or those books in detail? Обсуждали план или книги подробно? Альтерн. вопрос.
Did my friends discuss their plan in detail, didn't they? Вопрос с хвостиком