TOEFL Listening: TPO-TOEFL阅读TPO - 3486R3YTYY46GN99N$

Why does the author discuss the Great Lakes in paragraph 5? A. To demonstrate the extent to which residence times vary from lake to lake B. To illustrate how residence times are calculated for specific lakes C. To argue that the residence time of a lake increases with area D. To emphasize that Lake Tahoe's residence time is unusually long