All the others are completely incorrect as Fortunato was completely sealed up so he isn't leaving. Montresor wasn't merciful to Fortunato as he is telling the story 50 years later with minimal regret if I remember correctly. Also, if Fortunato is only pretending to be sick, what effect does the have on the story's ending? He dies either way so pretending to be sick doesn't get him more of what he wants which is the cask of amontillado.
So, in short, I don't know A to be the answer as a fact but I have reasoned A to be the only logical answer.
