Reading Comprehension (RC) | Re: At the end of the nineteenth century, a rising interest

HelloGMATNinja ,
Could you please elaborate on the question and answer of question number 6 of the above passage

"38. It can be inferred from the passage that a characteristic of the ethnological research on Native Americans conducted during the nineteenth century was the use of which of the following?

(A) Investigators familiar with the culture under study
(B) A language other than the informant’s for recording life stories
(C) Life stories as the ethnologist’s primary source of information
(D)
...

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