How are fossil fuels formed over time?

The formation of fossil fuels is primarily a result of the accumulation of organic matter, which primarily comes from plants and animals, that has been buried under layers of mud and sand over millions of years. This organic matter undergoes a complex process involving heat and pressure, transforming it into coal, oil, or natural gas.

While the answer correctly highlights the role of organic matter and suggests the conditions under which these materials are found, it's worth noting that the intense heat and pressure specifically referred to in option A are part of the process that takes place after the organic material is buried. Thus, option B captures the initial step in fossil fuel formation, emphasizing the importance of organic matter being deposited and eventually transformed through geological processes.

The other options either misattribute the process to unwanted elements, such as radioactive materials in option D, or introduce incorrect mechanisms for fossil fuel formation, like chemical reactions between minerals and microorganisms in option C. This helps clarify the critical role that ancient organic remains play in fossil fuel formation.