Fossil fuels refer to

• A. Coal, oil, natural gas, and other fuels that are ancient remains of plants and animals.
• B. Any combustible material formed from fast-growing plants.
• C. Energy produced exclusively by hydroelectric power.
• D. A form of energy derived from the sun.

Answer: (C)

Fossil fuels are energy resources formed from ancient organic material. Coal, oil, and natural gas come from plants and animals that lived long ago; over millions of years, heat and pressure transformed buried remains into dense, carbon-rich fuels. They’re nonrenewable because their formation takes geological timescales, far longer than human use.

Other energy sources mentioned—hydroelectric power, biofuels from recently grown plants, and solar energy—do not fit fossil fuels. Hydroelectric relies on moving water, biofuels come from recent plant growth, and solar energy comes from the sun.