The correct answer is: A. Fermentation
Fermentation is the process of converting organic materials into simpler substances using microorganisms, typically yeasts or bacteria. Biogas is a gas produced by the breakdown of organic matter in the absence of oxygen. The main components of biogas are methane, carbon dioxide, and hydrogen sulfide. Biogas can be used as a fuel for cooking, heating, and electricity generation.
Biodegradation is the process of breaking down organic matter by microorganisms. Biodegradation is a natural process that occurs in the environment. It is important for the cycling of nutrients and the decomposition of waste.
Purification is the process of making something clean or pure. Purification can be done by physical, chemical, or biological methods.
Sedimentation is the process of settling of solid particles from a liquid suspension. Sedimentation is a natural process that occurs in the environment. It is important for the removal of pollutants from water.
In conclusion, the correct answer is: A. Fermentation.