grammatical number - Which one is correct for the usage of "s" suffix for multiple name exposition word case?

Assumed A, B, and C are book name, which one of the following sentence is correct for the usage of "s" suffix in "book" word?

1. Are the A, B, and C books inside the box?




2. Are the A, B, and C book inside the box?




3. Both 1 & 2 are correct.




4. Everything is wrong (then say something about it ^^)

Answer

Your 1) is grammatical, though it is a bit unusual. Normally you'd just say

Are A, B, and C in the box?

or if you didn't expect the hearer to recognise the names as book titles:

Are the books A, B, and C in the box?

Your 2) is not grammatical.

(I have changed inside to in in my examples. Inside is grammatical, but I would only use it if I was making a contrast, eg inside as opposed to next to the box.)