TOEFL Reading: ETS-TOEFL阅读机经 - GTTFBUB3I310Q43YL$

According to paragraph 1, what do ethologists think is the most notable characteristic of animal behavior? A. Animal responses in most situations are predictable and do not vary B. In similar situations, different animal species often behave in similar ways. C. Even in ordinary situations, animal behavior can be unusually complex. D. Animal behavior may sometimes include stimulus/response reactions.