Which sentence from the story best indicates the unreliability of the narrator?

a. "i was never kinder to the old man than during the whole week before i killed him. "

b. "to think that there i was, opening the door, little by little, and he not even to dream of my secret deeds or thoughts."

c. "no doubt i now grew very pale; – but i talked more fluently, and with a heightened voice. "

d. "i swung the chair upon which i had been sitting, and grated it upon the boards, but the noise arose over all and continually increased."