A. The dialogue in which Mrs.Hale explains what is hidden in Minnie's box
I believe the correct answer is naive.
The author is trying to say that he was ignorant, and that he couldn't understand properly these new revelations. He was either too young or too stupid to understand such a thing, but he believes he will as he grows older.
Monologue is spoken by one character, usually to themselves.
Dialogue is spoken by multiple characters