TOEFL Listening: TPO-TOEFL阅读TPO - Z3565B1ZB9DZ88D0N$

The phrase "So much" in the passage refers to A. the negative effects of overland flow, rain, and evaporation on river water levels B. water that a lake loses to outflowing rivers, to the lake bed, and to evaporation C. the importance of rivers to the maintenance of lake water levels D. the information given about ways that water can enter or exit a lake