TOEFL Reading: ETS-TOEFL阅读机经 - A7H364ANP85O4J51L$

Why does the author include the information that Mayan cities had "flourished for over 500 years and had frequently been at war with each other?" A. To identify a possible reason for the eventual collapse of Mayan society B. To make the point that war and social unrest alone do not account for the Mayan collapse C. To explain why recent studies argue that human actions were responsible for the Mayan collapse D. To provide evidence that frequent wars weakened Mayan society only very gradually