Question

Scholars who once thought Native American literatures were solely oral narratives recorded by missionaries or anthropologists now understand this body of work to consist of both oral literatures and the written works of Native American authors, who have been publishing since 1772.

Answer 1

Answer:

(A) Scholars who once thought Native American literature's were solely oral narratives

Explanation:

The question is not the relative pronoun-that-or idiom-either. It's more about modifying oral narratives and how it's combined with its modifier-recorded by.

You can't combine this modifier with its modified noun-narratives-with an and.  

A. Scholars who once thought that Native American literature's were just oral narratives = The modified noun sitting right next to its modifier is correctly modified.