TOEFL Reading: ETS-TOEFL阅读机经 - 934XQ3X7I0PQOB0SL$

The purpose of paragraph 7 in the passage is to A. provide evidence that soils in equilibrium maintain nutrients for longer periods of time than other soils B. explain why geologically youngersoils are more fertile than older soils, regardless of where they are found C. explain how long it takes for soils to develop and what elements affect their fertility D. summarize the various stages of soil formation discussed earlier in the passage