Answer:
D. We know that silvers doesn’t mean it but the narrator doesn’t
Explanation:
Dramatic irony is the kind of irony where the narrator is unaware of some detail in the story but the audience are in the know.
Therefore, when the narrator in "Treasure Island" states that Long John Silver clapped him on the shoulder "in the friendliest way", the dramatic irony in this description is that the readers know that he does not mean it but the narrator doesn't.
