Answer:
C. Coal
Explanation:
Coal is a fossil fuel that develops from remains of ancient organisms. Death of plants and their subsequent burying in ground initiates the process of coal formation. Anaerobic conditions do not allow the bacteria and fungi to decompose the wood completely. The buildup of heat and pressure on partially decomposed wood converts them into coal over a long period of time. Since coal formation is a slow natural process, it is a non-renewable energy source with limited supply.