D) The book market is rather slack.

D）图书市场相当疲软。

They are, in fact, some of the best-selling books in the U.S. book market.

事实上，它们是美国图书市场上的一些畅销书。

But it wasn’t just about cheap paper and tiny, mass market size books.

但这不仅仅是廉价的纸张和体积小的大众市场尺寸的书籍。

In fact, the digital book market overall, which includes audiobooks, e-book sales and subscriptions to various reading devices, showed a very good growth across the year.

事实上， 整个数字图书市场，包括有声读物、电子书销售和各种阅读设备的订阅，全年都呈现出非常好的增长势头。