Recent living matter or by-products of its decomposition used as an energy source is called a

• A. Fossil fuel
• B. Wind energy
• C. Geothermal
• D. Biofuel

Answer: (D)

Biofuels are fuels produced from recently living matter or the by-products of its decomposition. This makes them renewable, since the biological material can be replenished or continually produced, unlike fossil fuels which come from ancient organic matter formed over millions of years. Examples include ethanol from crops, biodiesel from vegetable oils, and biogas from the anaerobic digestion of organic waste. In contrast, wind energy uses the kinetic energy of moving air, and geothermal energy taps heat from within the Earth, while fossil fuels rely on ancient organic deposits. Because the definition centers on energy derived from current or recently processed biological material, biofuel is the best fit.