The paragraph is followed by an incomplete phrase or sentence which summarizes the main idea of the paragraph. Choose the missing words of the phrase or sentence.

The oil drilled and pumped from underground holds the energy of eons’ worth of sunlight energy collected by plants and stored as organic matter. Over millions of years of heat and pressure, the energy in that organic matter has been further concentrated to yield hydrocarbons such as oil, natural gas, and coal.
（） of fossil fuels.