If coral reefs are made up of the exoskeletons of thousands of tiny polyps, then coral reefs are made up of the exoskeletons of thousands of what?

Answer choices:
- Absorb light
 - scarce resources
 - Chlorophyll
 - tiny polyps
 - to stay warm
 - animals
 - salt and water.
 - graptolites

 

    tiny polyps      