The correct option is C Methanogenic bacteria
Anaerobic digestion is a natural process in which bacteria convert organic materials into biogas. It occurs in marshes and wetlands and in the digestive tract of ruminants. The bacteria are also active in landfills, where they are the principal process degrading landfilled food wastes and other
biomass. Biogas can be collected and used as a potential energy resource. The process occurs in an anaerobic (oxygen-free) environment through the activities of acid- and methane-forming (methanogenic) bacteria that break down the organic material and produce methane and carbon dioxide in a gaseous form, known as biogas.