The Lord of the Rings is one book, actually. It just got published in three volumes so that they could space the book out over a few years (this was back in the paper shortages around WWII that made the massive book being published all at once a bad idea). So I don't think you need to worry about changing it. Good quiz too, I was surprised at how many of these I'd never heard of before.
I tried the Fellowship of the Ring. If you're going to say no series, I would at least accept the individual book titles.