TOEFL Reading: ETS-TOEFL阅读机经 - 51Q72NTX75YXN17UL$

Why does the author point out that on Earth "gases in the atmosphere or water react with rocks at the surface to form new chemical components?" A. To explain why scientists believe that few areas on Earth have been untouched by flowing water B. To identify one of several ways in which the movement of fluids can affect the surface of a planet C. To provide evidence that fluid movements are caused by gravity flow systems energized by the Sun D. To identify an effect of wind scouring fine particles away from large areas