Answer:
C and D have the same answer?? wdym
Explanation:
A coral reef is a complex [ecosystem] of calcium carbonate shells that are home to microbes, algae, invertebrates, and fishes, and its high productivity helps provide great species richness.
Because the people that mae them wanted them to be very small
If by inadequate you mean not meeting the necessary levels (too low), then it is "hypo"