I will vote for A and not D because
Ans choice A
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.
main Clause -
Scholars {subordinate clause} now understand this body of work to consist of both oral literatures and the written works of Native American authors
subject: Scholars
Verb: understand
subordinate clause -
who once thought Native American literatures were solely oral narratives recorded by missionaries or anthropologists
Subject: Who --> refers to Scholars from main clause
verb: were
the verb-ed modifer "recorded" refers to narratives
Subordinate clause -
who have been publishing since 1772 - Here "who" refers to the Scholars
Subject: Who refers to Scholars from the main clause
Verb: have been publishing
Ans Choice D
Native American literatures, which some scholars once thought 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.
main clause -
Native American literatures, {subordinate clause} now understand this body of work to consist of both oral literatures and the written works of Native American authors
subject - Native American literatures
verb - understand
Native American literatures understand -> wrong doesnot make sense
subordinate clause -
which some scholars once thought were solely oral narratives recorded by missionaries or anthropologists
Subject - Which - refers to Native American literatures from main clause
verb - were
subordinate clause -
who have been publishing since 1772
subject - who - refers to Native American literatures from main clause
verb - works
Native American literatures works -> wrong doesnot make sense