Many corals secrete an exoskeleton that builds up to become a coral reef, and good examples are Bubble coral, Elegance coral, Frogspawn and other Euphyllia corals. Given these facts, what is secreted by organisms like frogspawn to become a reef among the following options:
- exocrine glands
 - food and shelter
 - exoskeleton
 - bones
 - Energy
 - Chemical energy
 - plasma
 - Energy.


 

   exoskeleton      