【单选题】Coral reefs are one of the most fragile, biologically complex, and diverse marine ecosystem on Earth. This ecosystem is one of the fascinating paradoxes of the bio- sphere: how do clear, and thus nutr...
A.
describing the effects of human activities on algae in coral reefs
B.
explaining how human activities are posing a threat to coral reef communities
C.
discussing the process by which coral reefs deteriorate in nutrient-poor waters
D.
explaining how coral reefs produce food for themselves
E.
describing the abundance of algae and filter-feeding animals in coral reef areas