Made from old plants and animals, it takes millions of years to form.

• A. Oil Sands
• B. Biomass Energy
• C. Oil and Gas
• D. Nuclear Power

Answer: (C)

Fossil fuels form from ancient organic matter that has been buried and subjected to heat and pressure for millions of years. Plants and animals from long ago died, their remains were preserved underground, and over vast geological timescales these remains transformed into hydrocarbons such as oil and natural gas. That long formation process is the defining feature of fossil fuels, making oil and gas the best match.

Biomass energy uses recently living material and is considered renewable on human timescales, so it doesn’t fit the “millions of years” idea. Nuclear power is based on uranium, not ancient plants and animals. Oil sands are also formed from ancient organic material, but the clearest and most direct reference to the usual long-term formation of fossil fuels points to oil and gas.