Which one of following is correct order of conversion of waste materials during biogas formation?

Biogas is made from the microbial degradation of organic matter under anaerobic conditions. The organic matter is present in the form of polymers which includes carbohydrates, fats and proteins. These are broken down into monomers such as sugars, fatty acids and amino acids respectively. The next step is acidogenesis and acetogenesis in which small inorganic acids are formed. The final step is methanogenesis resulting in the formation of biogas that is a mixture of gasses such methane and carbon dioxide. This biogas can be used as fuel for various processes. Thus the correct answer is option D.