GMAT Sentence Correction (SC) | Researchers have explored the possibility that dolphins

D is absolutely not correct. There's a big difference between "as humans" (meaning "in the role of humans") and "as humans do" (meaning "in the same way as humans"). E is the only viable answer. Don't let the word "being," which often serves as a red flag for awkward constructions, immediately put you off of any answer. There are certainly better ways than E to express the thought (how about "can be trained to communicate"?), but all