The most accurate statement regarding the common formation of all fossil fuels is:
"One living organisms are converted into carbon-rich fuels."
Fossil fuels, including coal, oil, and natural gas, are formed from the remains of ancient living organisms (primarily plants and marine organisms) that have undergone chemical and physical changes over millions of years under heat and pressure. While specific environments (such as swampy areas for coal or oceanic conditions for oil) play a role in the type of fossil fuel formed, the essential process involves the transformation of biological material into carbon-rich energy sources.