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a combustible black or dark brown rock consisting mainly of carbonized plant matter, found mainly in underground deposits and widely used as fuel; nonrenewalbe fossil fuel
a gas usually found above petroleum deposits and burned to obtain energy, a non-renewable fossil fuel
a resource that uses organic matter such as plants, wood, and waste; it is burned to release energy.
a natural resource that can be converted by humans into other forms of energy in order to do useful work
the practice of finding ways to use less energy or to use energy more efficiently
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