Answer;
Fossil fuels
On a global basis, fossil fuels form the largest reservoir of carbon.
Explanation;;
Carbon dioxide gas is found in the atmosphere, carbonate rocks that are found in many locations on Earth and carbon-based fossil fuels that are found deep on the Earth.
-The major reservoirs of carbon include, the atmosphere, terrestrial biosphere, the ocean, the sediments (such as fossils fuels, fresh water systems) and the Earth's interior.
-The carbon exchanges between reservoirs occur as the result of various chemical, physical, geological, and biological processes.
-The ocean contains the largest active pool of carbon near the surface of the Earth.