"There are very many chapters in the book."
Translation:Plurimae lectiones in libro sunt.
Lectiones, are feminine.
Plurimi is always plural, when you have several items.
Plurimus, the singular, would be used for a quantity I guess.
Here it's the nominative.
Plurimi is the masculine.
Plurimae is the feminine.
Plurima is the neutral.
plurimes doesn't exist.
"very many" needs to be dropped. (Please see my more substantive comments on this topic elsewhere in this lesson.) It's not okay. And I'm going to keep posting comments until it's fixed because DL staff not only hasn't corrected this but is arguing with people. I've never seen anything like this in any other DL course. Please don't be convinced otherwise. You should not be using the phrase "very many" in English. There are a plethora of better options