Poe has a plan for the plot, and that is revenge. Plot means the action you can expect. None of the other answers engage you in the plot. Answer (“… neither by word nor deed had I given Fortunato cause to doubt my good will.”) describes Fortunato, not the plot. Answer (“… this was a point not definitively settled.”) is an incorrect version of the sentence. Answer (“I have my doubts.”) is a word play the narrator uses to entice Fortunato.