Fact 1: Corals form large colonies in shallow tropical water. Fact 2: Coral reefs are made up of the accumulated exoskeletons of the coral polyp. Given the two facts above, answer the question "What forms in shallow tropical water?" with the following options: - blobfish - sub-units of species - accumulated exoskeletons - aqueous solution - polar bears - an area swollen with pus - swamp vegetation - deep-sea dwellers
A:
accumulated exoskeletons