Which is the most important reason to continue efforts to preserve coral reefs

Coral reefs support a wide variety of organisms. They are very sensitive and are a main part in the ocean life. 
a.
Coral reefs are a valuable commodity in the aquarium business.
b.
Coral reefs support a wide variety of organisms.
c.
Coral reefs are one of the oldest ecosystems.
d.
Coral reefs are important for marine recreation.

Its B Coral reefs support a wide variety of organisms.

Ijust took the quiz. their is no coefficient needed. : )