Correct Answer: fermentation

Solution : The correct option is fermentation .

Anaerobic fermentation is a naturally occurring biological process that produces biogas. In the absence of oxygen, microbes break down organic waste, animal dung, sewage, and other organic stuff during this process. Methane (CH ₄ ) and carbon dioxide (CO ₂ ) are the main gases produced by this fermentation. Biogas is a renewable energy source that may be harvested, collected, and used for a variety of tasks, such as heating, cooking, generating power, and fueling automobiles.