TOEFL Reading: ETS-TOEFL阅读机经 - 63ZAC3345L474IMEL$

According to paragraph 3, one important physical effect of compost is that it A. adds an oxygen-rich layer to the layers rich in nitrogen and carbon B. decreases the quantity of plant material that needs to be discarded C. helps keep the same amount of moisture in each layer of soil D. reduces the amount of fungi and aerobic bacteria in the pile