The correct answer for this question is this one: "c. He does not offer any possible reason for wanting to murder fortunato." In Poe's the cask of amontillado because of the reason that he does not being offered with any possible reason makes Montresor or unreliable narrator.
Here are the following choices:
a.he is part of a secret association
b.he makes exaggerated claims about fortunato
c.he does not offer any possible reason for wanting to murder fortunato.
