Well, just the fact that the characters are all dressed up for a masquerade party, already adds to the eerie mood. But what really seals the coffin is when Montressor lures Fortunato into the catacombs, and then ties him up. You really get the whole creepo-vibe, when Montressor starts to seal up the "tomb". Hope this helps you a lot.
I can help you with your essay. i have done one like that before.
The answer is C.during the civil war
