Many scientists believe that the human brain, despite its complexity, still has areas that remain largely unexplored, and they are continuously developing new techniques to study it.

The correct answer to the question "Many scientists believe that the human brain, despite its complexity, still has areas that remain largely unexplored, and they are continuously developing new techniques to study it." is Option C: still has areas that remain largely unexplored, and scientists are continuously developing new techniques to study them..

The other options — A) still has areas that remain largely unexplored, and they are continuously developing new techniques to study it., B) still have areas that remain largely unexplored, and they are continuously developing new techniques to study them., D) still has areas that largely remain unexplored, and developing new techniques to study it continually. — are incorrect for this GMAT Exam Prep question. As explained above: The pronoun 'it' in the original sentence refers ambiguously to 'the human brain' rather than 'areas'. Replacing 'they' with 'scientists' and 'it' with 'them' clarifies the subjects and ensures corre…