The correct answer is:
A. Large amounts of organic matter were buried and then trapped by underground rock formations to create petroleum reservoirs.
This option accurately describes the geological processes that lead to the formation of petroleum. Petroleum originates from the decomposition of organic materials (primarily microscopic marine organisms) that are buried under layers of sediment. Over millions of years, heat and pressure transform this organic matter into hydrocarbons, which accumulate in rock formations to form petroleum reservoirs.