TOEFL Listening: TPO-TOEFL阅读TPO - JM1807F9PY8F4A1GN$

In paragraph 1, why does the author mention "the pressure of the overlying rock"? A. To show how water can be forced deep under Earth's surface B. To show why groundwater is more plentiful than surface freshwater C. To correct a commonly made error about the location of groundwater D. To explain why most groundwater lies near Earth's surface