Answer:
B. the guilt of the narrator
Step-by-step explanation:
This question refers to Edgar Allan Poe's short story "The Tell-Tale Heart".
The narrator decides to kill the old man with whom he lives, for no apparent reason other than the old man's "pale, vulture-like eyes".
After killing the man, dismembering his body and hiding the remains, the narrator is convinced he had committed a perfect crime. However, when the police arrives to investigate the case, he starts to hear the sound of the beating heart louder and louder. He associates this with the sound of the dead man's heart, which is of course highly unlikely. Instead, the sound he hears is most likely sound of his own heart increased in intensity in his distorted, guilt-consumed mind.