Answer:
The effect an unreliable narrator has on the reader is A. to make the reader question the narrator's credibility and trustworthiness.
Step-by-step explanation:
"Unreliable narrator" is a term coined in 1961 by Wayne C. Booth. It refers to a narrator - most of the times a first-person one - who is incapable of telling the story without any bias. The narrator is either somehow impaired, unable to understand facts and reality, or biased, misjudging behaviors and situations according to his/her own opinion.
One of the most famous literary works in Brazil, "Dom Casmurro" by Machado de Assis, is to this day considered a major example of an unreliable narrator. The narrator, Bentinho, is sure of his wife's infidelity and the only two reasons he presents for that are her deceiving eyes and her determination to get what she wants. By the end of the novel, it is impossible for the reader to know what really happened, since every detail presented has been tainted by Bentinho's opinion.