Many corals secrete an exoskeleton that builds up to become a coral reef, and australia's coral reefs, including the Great Barrier Reef, are no exception. Given these facts, what was formed by exoskeletons among the following options:
- heat produced
 - remains of prehistoric life
 - layers of fat
 - The area was once underwater
 - the Great Barrier Reef
 - the body's largest organ
 - sedimentary rocks
 - it keeps an organism warm


 

     the Great Barrier Reef    