What's an appropriate conversational response to 这是什么？ In English, if someone points to a book and says "What's that?", "A book" is a sufficient reply. In Chinese, if someone points to a book and says "这是什么？", can you say "书" or maybe "一本书"? What's the most natural and conversational response?
Most often, I would repeat 这是, so if you would ask me 这是什么? I would say 这是一本书. You can also say 一本书. But you can also just say 书.