Which excerpt from "the tell-tale heart" best illustrates that the narrator is unreliable

a. true! —nervous—very, very dreadfully nervous i had been and am; but why will you say that i am mad? the disease had sharpened my senses—not destroyed—not dulled them. above all was the sense of hearing acute.”

b. “his room was as black as pitch with the thick darkness, (for the shutters were close fastened, through fear of robbers,) and so i knew that he could not see the opening of the door, and i kept pushing it on steadily, steadily.”

c. “presently i heard a slight groan, and i knew it was the groan of mortal terror. it was not a groan of pain or of grief—oh, no! —it was the low stifled sound that arises from the bottom of the soul when overcharged with awe.”

d. “i smiled,—for what had i to fear? i bade the gentlemen welcome. the shriek, i said, was my own in a dream. the old man, i mentioned, was absent in the country. i took my visitors all over the house.”