______ formed by the buried remains of small plants and animals.

We must first comprehend what fossil fuels are in order to respond to this query. Decomposition of living things yields fossil fuels. These fuels, which contain carbon and hydrogen and are present in the Earth's crust, can be burned to produce energy. Coal, oil, and natural gas are a few examples of fossil fuels. By heating this substance, thick oil that can be used to make gasoline is created.
Biogas is a biological substance that originates from living or non-living plants or animals. This substance can be burned to produce a renewable energy source, such as forest residues. Although biogas can be refined and used as an energy source, it does not have as much methane as natural gas.
A fossil fuel is petroleum, also referred to as crude oil. Petroleum was created from the remains of extinct marine organisms like plants, algae, and bacteria, just like coal and natural gas.
Hence, option 4 is correct.