TOEFL Reading: ETS-TOEFL阅读机经 - WL7G3N0UAH443N62L$

According to paragraph 5, why does soil material tend to be drier on steep slopes than on flatter land? A. Steep slopes are less likely to experience soil creep. B. Soil material on steep slopes tends to be thicker. C. Water that falls on steep slopes tends to erode the soil there and deposit it on level ground. D. More water runs off steep slopes before it can enter the soil.