Explanation:Fossil Fuels:Fossil fuels are formed by natural processes such as anaerobic decomposition of buried organisms under heat and pressure.Fossil fuels like coal, petroleum, natural gas contain high percentages of carbon.Fossil fuels are non-renewable resources and must be burned to release their energy.It releases sulphur, nitrogen, carbon, etc. gases in the atmosphere which causes the greenhouse effect and pollution.The correct answer is Wood.Some exhaustible natural resources like coal, petroleum and natural gas,These were formed from the dead remains of living organisms (fossils).So, these are all known as fossil fuels.Coal is one of the fuels used to cook food.Earlier, it was used in railway engines to produce steam to run the engine.It is also used in thermal power plants to produce electricity. Coal is also used as fuel in various industries.Petroleum was formed from organisms living in the sea.As these organisms died, their bodies settled at the bottom of the sea and got covered with layers of sand and clay.Over millions of years, absence of air, high temperature and high pressure transformed the dead organisms into petroleum and natural gas.A natural fuel such as coal or gas, formed in the geological past from the remains of living organisms.Unlike coal or crude oil, wood does not remain of a prehistoric organism, and therefore it is not fossil fuel - it's just fuel.