This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
[{'content': 'The biological oxygen demand (BOD) indicates \nSelect and explain. \nA. Organic matter, B. Bacterial content, C. Anaerobic bacteria, D. Chemicals', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Biological Oxygen Demand (BOD): Is defined as ‘amount of oxygen absorbed by a sample of sewage’ during a specified period (Generally 5 days), at a specified temperature (generally 20° C) for aerobic destruction or use of organic matter by living organisms.\nStrong Sewage has BOD > 300 g/litre and Weak Sewage has BOD < 100 g/litre.', 'role': 'assistant'}]