In "The Cask of Amontillado," the sentence that uses dramatic irony to show Fortunato's unawareness of the danger ahead is:
D. “Enough,’ he said; ‘the cough is a mere nothing; it will not kill me.’” (paragraph 30)
This line exemplifies dramatic irony because the reader is aware that Fortunato is in a perilous situation with Montresor, who has sinister intentions, while Fortunato dismisses his illness, not realizing the true danger he is in.