TOEFL Listening: TPO-TOEFL阅读TPO - QSXMPB10FI3MJ235N$

In paragraph 1, what does the author imply about changes in the African environment during this time period? A. The climate was becoming milder, allowing for a greater variety of crops to be grown. B. Although periods of drying forced people south, they returned once their food supply was secure. C. Population growth along rivers and lakes was dramatically decreasing the availability of fish. D. A region that had once supported many people was becoming a desert where few could survive.