Bunuel wrote:
Everyone participating in the early sociological study committed a crucial methodological error by failing to fully consider alternative ways of classifying their data.
(A) by failing to fully consider alternative ways of classifying theirRedundancy & not quite as polished as answer choice (D)"Everyone committed an error by failing to [...]"
You'd expect something along the lines of
"Everyone committed an error by doing/not doing XYZ"
(B) by failing fully to consider alternative ways of classifying theirFailing fully changes the intended meaning, and I'm not even sure how saying "Failing fully" makes much sense(C) they failed to consider alternative ways to classify theirthis is missing "by", which is needed for the sentence to make sense(D) by not fully considering alternative ways to classify theLooks o.k(E) by not considering fully alternative ways of classifying his or her"Fully alternative" doesn't make much sense & changes the meaningI feel like I might be missing something with the pronoun "Their", but I'm not quite certain. Very interested in seeing the explanation for the question.