TOEFL Reading: ETS-TOEFL阅读机经 - 352KOP3U0BLZ5N30L$

Why does the author include the information that "some small, less social odontocetes such as Indus river dolphins echolocate well but do not possess the exceptionally large brains that bottlenose dolphins do?" A. To argue that in odontocetes, sociality determines whether an animal has a large brain. B. To argue that echolocation does not necessarily involve exceptionally fast auditory brain stem responses to sounds. C. To help explain why effective echolocation does not necessarily require extreme development of the auditory system. D. To provide evidence that weakens the theory that the large brains of bottlenose dolphins are explained by their need to echolocate.