A credible narrator or reliable narrator will tell the story from the point of view of the truth, it does not matter if she or he has any attachment to what is going on in the story, readers can trust their words and understand the circumstances the way they the story unfolds. On the other hand, the unreliable narrator will tell their story from their point of view, they will embelish their deeds, hide or down play their problems, therefore the reader will always have the impression that the unreliable narrator is conducing the reader to trust them.
The crediable narrator will bring the facts to the reader and put the reader in the story, the reader can have the feeling of engagement on the narration. On the other hand, the unreliable narrator brings the uncertainty feeling tothe reader and the reader can dot the i's as they please because they know they cannot fully trust the narrator.
Not 100% sure but I think it’s D. Figurative language is a way of describing that uses figures of speech and imagination.
