Answer:
B) he heard the old man's heart
Step-by-step explanation:
The narrator heard his heartbeat but thought that it was the old man's heart beating. He thought that the police would figure out there was a body around them so he confessed.
''He couldn't stand the horror any longer because he knew that "they were making a mockery of my horror . . . [and] anything was better than this agony!" Thus, as the beating of the heart becomes intolerable, he screams out to the police: "I admit the deed! — tear up the planks! here, here! — it is the beating of his hideous heart!" ''
'' His heart rate was so fast to the point that his heartbeat was pounding in his ears so loudly that he could not stand the psychological pressure any longer. Thus he confesses to his horrible deed. The narrator's "tell-tale" heart causes him to convict himself.''