TOEFL Reading: ETS-TOEFL阅读机经 - 5432Y33F1V1M7UV5L$

In paragraph 4, why does the author discuss the effects of removing plant-eating fish and sea urchins from coral reefs? A. To identify a situation that contributes to the dominance of corals in shallow waters B. To demonstrate the importance of grazing on seaweeds for the survival of some corals C. To provide evidence that seaweeds are better competitors than coral at depth D. To argue that sea urchin pathogens also attack corals