The answer is: A. to point out details the character would not notice.
The first-person point of view is a literary device that allows readers to get to know that character's thoughts, feelings and motives. Because the narrator refers to himself with words like I, me, my and mine, the story is seen through his or her eyes. As a consequence, it is not impartial and it may suggest features which are unknown or unnoticeable to the narrator. For example, they might not realize they have a psychological condition.