How does the use of dramatic irony in works with unreliable narrators to make the purpose of the story clearer to the reader?

Well I'm guessing that I can pick out of these answers: a. It helps the reader understand the implications of events better than the narrator could.
b. It makes the story more interesting for the reader by adding a layer of mystery.
c. It allows the reader to understand and better relate to the motivations of the narrator.
d. It allows the reader to cast judgment toward the narrator in the story.
e. It indicates the thoughts of the narrator and other characters more clearly to the reader.

// I've seen this question before on plato

Out of all of them the correct answer is c. It allows the reader to understand and better relate to the motivations of the narrator.