Answer:
The correct answer is underneath the Earth's surface or in the crust layer of Earth.
Explanation:
Fossil fuels are the combustible organic materials like coal, natural gas, crude oil which are formed from the deposits of the decayed parts of the animals and plants which died millions of years ago while reserves are the deposits of these natural resources like minerals, elements and fuel.
Fossil fuels are usually found underneath the Earth's surface or in the crust layer of Earth at varying depths.
Thus, underneath the Earth's surface or in the crust layer of Earth is the correct answer.
