TOEFL Listening: TPO-TOEFL阅读TPO - 50BA4SC5S04EL1RBN$

Why does the author use the phrase "Note the word 'net'" in the passage? A. To emphasize the impact of seepage on water levels B. To point out that seepage is calculated differently from river flows and atmospheric exchanges C. To compare the different methods of calculating seepage D. To emphasize the difficulty of obtaining specific values for seepage inputs and outputs