TOEFL Reading: ETS-TOEFL阅读机经 - 60R354NT5E431F5TL$

Why does the author describe how some cricket species "maximize the volume of their calls?" A. To argue that crickets are a major source of noise in virgin rain forests B. To help explain why it is difficult for many smaller animals to be heard in rain forests C. To help explain why rain forests are noisier than other natural environments D. To illustrate a sophisticated way of making a call heard in a rain forest