This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and health, Subject name: Social & Preventive Medicine
[{'content': 'All are components of Sewer gas except - \nSelect and explain. \nA. H2S, B. CO2, C. SO2, D. Methane', 'role': 'user'}, {'content': "Answer: C \nExplanation: When the sewage is highly concentrated and contains plenty of solids the anaerobic process is highly effective. The end products of decomposition are methane, ammonia, CO2, and H2S. Park's Textbook of Preventive and Social Medicine, 25th Edition, Pg 794", 'role': 'assistant'}]