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.
A.Scholars who once thought Native American literatures were solely oral narratives
B.Scholars thinking of Native American literatures once solely as oral narratives, and
C.Scholars who once had thought of Native American literatures solely as oral narratives and
D.Native American literatures, which some scholars once thought were solely oral narratives(A)
E.Native American literatures, which some scholars once, thinking they were solely oral narratives
这道题目答案是选A，但是thought面跟的是一句宾语从句，宾语从句的that不是不能省略的吗？这里怎么可以呢？
