What transformation retains the meaning of comparing two books?

The transformation that best retains the meaning of comparing two books is found in the choice that states one book is not as interesting as the other. This statement effectively communicates a comparison between the two books by highlighting their relative interestingness.

In this case, it provides a direct comparative structure where the listener or reader can clearly understand that one book is perceived as less interesting compared to the other. Such a comparison is essential to convey the intended meaning of evaluating the interests generated by each book.

The ability to articulate this relationship using a negative phrasing also emphasizes the distinction without reversing the focus, which is critical for maintaining the essence of comparison. By using "not as interesting," the sentence succinctly conveys that while both books are interesting, one falls short in comparison to the other.

Overall, this clarity in expressing the comparison makes this particular transformation the most effective choice.