In Tell Tale Hart story, what causes the conflict between the narrator and the old man?

A
The narrator and the old man resent having to live together because of the narrator’s disease, and so the narrator decides to murder the old man.
B
The narrator is driven mad by the sound of a heart beating beneath the floorboards, and this causes him to kill the old man.
C
The narrator watches the old man sleep, and when the terrified old man discovers this, the narrator kills him to keep his madness hidden.
D
The narrator is terrified of the old man’s blue eye and overwhelmed by the sound of his heartbeat, so the narrator kills the old man.