Answer:
a. Narrative pattern
Explanation:
A narrative pattern is a literary style where a story is told by presenting connected events in a sequential manner.
Though Irving's story is fictional, the use of Knickerbockers' frame story creates a narrative pattern. The story identifies Knickerbocker as the supposed author. Irving used fictional narrators, allowing him to distance himself from the story. This made him act as a narrator reporting a story that was told to him thereby avoiding scrutiny because the supposed author no longer lives.