TOEFL Listening: TPO-TOEFL阅读TPO - R54F9UU0A230A5KSN$

According to paragraph 2, what was it that brought cattle and humans into close association? A. The development of smaller breeding units within hers B. Cattle and humans staying close to permanent water supplies for long period of time. C. The development of greater discipline among cattle. D. Cattle and humans constangly on the move searching for food and reliable water supplies.