Studies have indicated that the human brain, which is an organ whose complexity is unparalleled in the natural world, requires a disproportionately high amount of the body's total energy intake to function.
Correct: B
The original sentence contains wordiness and redundancy in the descriptive clause 'which is an organ whose complexity is unparalleled in the natural world.' Option B, 'an organ of unparalleled complexity in the natural world,' is a concise and grammatically correct appositive phrase that efficiently conveys the same meaning without unnecessary words. This makes the sentence more direct and readable, which is preferred in GMAT Sentence Correction. Option C incorrectly changes the main verb 'requires' to a participle 'requiring,' creating a sentence fragment (lacking a main verb for 'brain'). Options A, D, and E are all more verbose or grammatically less precise. Option D is clunky and less direct ('the complexity of which'). Option E adds 'and requires,' changing the structure to make 'brain' the subject of two separate verbs connected by 'and,' but the description remains wordy.