Question

plants and ______ are major carbon reservoirs.
water
fossil fuels

Explanation:

Both water and fossil fuels are significant carbon - containing entities. Water can dissolve carbon - containing compounds and has a large capacity to store carbon in the form of dissolved inorganic carbon and organic carbon. Fossil fuels like coal, oil, and natural gas are formed from the remains of ancient organisms and are rich in carbon.

Answer:

Both water and fossil fuels are correct. So the answer is: water, fossil fuels.