I think its B. seashells?
Explanation:
Organisms in the ocean take Carbon Dioxide and turn it into carbonate CO 2/3
Carbonate is often combined with ions like CA 2+ and MG 2+
The Calcium Carbonate makes up the hard structures of corals, and sea shells. The amount of Carbon in the Coral reefs far exceeds the amount of Carbon Dioxide dissolved in the oceans.
