The correct answer is C. The narrator says he is not mad, but he claims he can hear all the sounds on heaven and earth.
Explanation:
An unreliable narrator is a type of narrator (usually a first-person narrator) who cannot be trusted by the reader, this means the narrator's words are not completely accurate or credible usually because the narrator is mentally ill, too naive, evil, forgetful or just dishonest. This features can be shown immediately in the story of literature work with an unreliable narrator or might be developed during the story. In any of the cases, the way the events are told by an unreliable narrator lack credibility.
Considering this, in the excerpt from "The Tell-Heart" by the American writer Edgar Allan Poe the reader can determine the narrator is unreliable as this narrator shows some symptoms of madness that are mainly expressed by the narrator claiming he is not mad, but need providing an illogical explanation as he mentions he had a disease but this disease makes him able to hear all the things in heaven, earth and hell " I heard all things in the heaven and in the earth. I heard many things in hell", which seems absolutely insane as the reader knows this is not possible and the narrator is contradicting himself by saying he is not insane and then providing an irrational and absurd explanation. Thus, the statement that best explains how the reader can determine that the narrator of this passage is unreliable is that the narrators say he is not mad, but he claims he can hear all the sounds on heaven and earth which cast doubts on the narrator mental health.