3. The author refers to "filter-feeding animals" (line 20) in order to

　　(A) provide an example of a characteristic sign of reef deterioration

　　(B) explain how reef communities acquire sustenance for survival

　　(C) identify a factor that helps herbivore populations thrive

　　(D) indicate a cause of decreasing nutrient input in waters that reefs inhabit

　　(E) identify members of coral reef communities that rely on coral reefs for nutrients

　　4. According to the passage, which of the following is a factor that is threatening the survival of coral reef communities?

　　(A) The waters they inhabit contain few nutrient resources.

　　(B) A decline in nutrient input is disrupting their symbiotic relationship with zooxanthellae

　　(C) The degraded waters of their marine habitats have reduced their ability to carry out photosynthesis

　　(D) They are too biologically complex to survive in habitats with minimal nutrient input.

　　(E) Waste by-products result in an increase in nutrient input to reef communities.

　　5. It can be inferred from the passage that the author describes coral reef communities as paradoxical most likely for which of the following reasons?
　   (A) They are thriving even though human activities have depleted the nutrients in their environment.

　　(B) They are able to survive in spite of an over- abundance of algae inhabiting their waters.

　　(C) They are able to survive in an environment with limited food resources.

　　(D) Their metabolic wastes contribute to the degra- dation of the waters that they inhabit.

　　(E) They are declining even when the water sur- rounding them remains clear.