Paragraph 1: Most of the world’s potable water——freshwater suitable for drinking——is accounted for by groundwater, which is stored in the pores and fractures in rocks. There is more than 50 times as much freshwater stored underground than in all the freshwater rivers and lakes of Earth. At greater depths within Earth, the pressure of the overlying rock causes pores and cracks to close, reducing the space that pore water can occupy, and almost complete closure occurs at a depth of about 10 kilometers. The greatest water storage, therefore, lies near the surface.
6. 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
At greater depths within Earth, the pressure of the overlying rock causes pores and cracks to close, reducing the space that pore water can occupy, and almost complete closure occurs at a depth of about 10 kilometers. The greatest water storage, therefore, lies near the surface.
在地球的更深处，上覆岩石的压力导致孔隙和裂缝闭合，减少孔隙水占据的空间，几乎完全闭合发生在约10公里的深度。因此，最大的蓄水量就在地表附近。
问为什么要提到the pressure of the overlying rock，原文已经解释了，就是为了说明地下水为什么靠近地球表面。
正确答案选D。