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.

The combination of the of two or more elements is known as a compound. 

A homogenous mixture has a uniform composition all throughout. They are similar in terms of the amount of composition present in a solution. For example, oxygen is diatomic, O2. So oxygen is a compound because it has 2 elements combined in it. It is also a homogenous mixture if there are a lot of O2 gases present in let’s say tank. They only differ in the place where they are present. A compound is a representation of one molecule whereas a homogenous mixture is present in a a solution.