First question:
The excerpt from "The Cask of Amontillado" which best infers what will be Fortunato's downfall is the following one:
"He had a weak point --this Fortunato --although in other regards he was a man to be respected and even feared. He prided himself on his connoisseurship in wine."
It infers Fortunato's downfall since Luchresi attracted his "friend" to the place where Fortunato was chained to a wall by putting Fortunato's connoisseurship in wine in doubt.
Second question:
The excerpt which is an example of foreshadowing is the following one:
"There were no attendants at home; they had absconded to make merry in honour of the time. I had told them that I should not return until the morning, and had given them explicit orders not to stir from the house."
It is an example of foreshadowing since the reader learns the two men will spend some time alone, and because at this point the reader already knows how Luchresi feels about Fortunato, it is not hard to think that things will end badly.
Third question:
The excerpt from "The Cask of Amontillado" which best summarizes the overall theme of the story is the following one:
"A wrong is unredressed when retribution overtakes its redresser. It is equally unredressed when the avenger fails to make himself felt as such to him who has done the wrong."
The theme is revenge in a very specific way: the person seeking it must make it clear to his victim the wrong that is being done is done by him or her, that is, the avenger. Otherwise, revenge becomes useless, according to the narrator.
Fourth question:
The excerpt from "The Cask of Amontillado" which presents the reader with the initial conflict of the story is the following one:
"The thousand injuries of Fortunato I had borne as I best could, but when he ventured upon insult I vowed revenge."
That is the initial conflict of the story, since it is a story of revenge. The narrator lets the reader know how he feels about Fortunato, and how strong that feeling is. Plus, the narrator tells the reader about his intentions of revenge.
