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

Fact 2: Coral reefs are made up of the accumulated exoskeletons of the coral polyp.

Given the two facts above, answer the question "what do coral polyps form?" with the following options: 
- lagoon
 - graptolites
 - a cuticle
 - barnacles
 - bioaerosols
 - cave
 - coral reef
 - salt and water.


 

       coral reef  