Answer:
D. are made of animals living symbiotically with simple algae
Step-by-step explanation:
Coral formations are made of animals living symbiotically with simple algae
The formation of Corals commenced when free-swimming coral larvae merges to submerged rock or other available surfaces along the edge of a island or continents.
Coral formation are generally divided in four classes by the scientist, They are:
1)Fringing reefs
2) Barrier reefs
3)atolls reefs
4)patch reefs