TOEFL Listening: ETS-TOEFL听力机经 - 1WLI421333JN43U9P$

What point does the professor emphasize when she discusses birds and their songs? A. Male birds often change the pace and pitch of their song to attract a mate. B. Birds are sensitive to small variations in their species' song. C. There is no proof that local dialects of birdsong affect behavior. D. There is no solid evidence that an individual bird's song changes over time.