Translate the sentence "This book is more difficult than that book" into Latin.

The translation "This book is more difficult than that book" into Latin necessitates using the comparative form of the adjective "difficult." In Latin, comparatives are commonly formed by modifying the root of the adjective, and in this case, the adjective “difficilis” (difficult) transforms into “difficilior” for the comparative sense, meaning "more difficult."

The phrase uses "hic liber" to indicate "this book" and "ille liber" to mean "that book." The structure "hic liber difficilior est quam ille liber" effectively communicates the comparative nature of the sentence, highlighting that one book surpasses the other in terms of difficulty.

The other provided options do not correctly convey the intended meaning. Using "facilior" conveys "easier," which is the opposite of what the sentence requires. The option with "difficile" lacks the comparative form, thus missing the comparative meaning entirely. Lastly, using "simplex" means "simple," which is unrelated to the intended comparison of difficulty.