What is the effect of the first-person narration in "there's a man in the habit of hitting me on the head with an umbrella"?

it leads the reader to belive that the narrator is unreliable, and thus, his story cannot be believed.
it lends a sense of believability to the absurd events, allowing the reader to suspend their disbelief.
it gives the story a unique perspective, since the narrator is not directly involved in the events of the plot.
it makes the story much less personal, allowing the reader to view it from an objective distance.

I believe the correct answer is B: It lends a sense of believability to the absurd events, allowing the reader to suspend their disbelief.

The point is to make an absurd story believable at the very basic, personal level. We may stop to think: but wait, how is it possible that someone is hitting another person with an umbrella all the time? But the story is supposed to make us ask ourselves who are we to doubt someone's personal account. The speaker had also had trouble to believe what's happening to him, and yet he got so used to it that now he can't imagine his life without his mysterious companion and his (somewhat bizarre) preoccupation.

So, by the time we finish reading the story, we already understand that (dis)believing should not be an issue at all.

Music me focus more because it blocks out all the distractions around me, but i guess it depends on who you are