Fact 1: Many corals secrete an exoskeleton that builds up to become a coral reef.

Fact 2: Hard corals build by secreting calcium carbonate skeletons.

Given the two facts above, answer the question "What constructs an exoskeleton using calcium carbonate?" with the following options: 
- animals
 - amoeba
 - sharks
 - insects
 - mammals
 - Man
 - coral
 - bats


 

       coral  