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': 'Biochemical oxygen demand is determined by \nSelect and explain. \nA. Oranic matter and bacteria, B. Oxygen content, C. Alage content in water, D. Agriculture fertiliser content in water.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. is \'a\' . Organic matter & Bacteria. "The strength of sewage is expressed in terms ofBiochemical oxygen demandChemical oxygen demandsSuspended solids demand""Biochemical Oxygen demand -It is the most important test done on sewage. It is defined as the amount of oxygen absorbed by a sample of sewage during a specified period, generally 5 days, at a specified temperature, generally 20 deg. G, for the aerobic destruction or use by organic matter and living organisms. BOD value ranges from about 1 mg per litre for natural waters to about 300 mg per litre for untreated domestic sewage. If the BOD is 300 mg/I and above, sewage is said to be strong ; if it is 100 mg/l, it is said to be weak."', 'role': 'assistant'}]