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 indicates - \nSelect and explain. \nA. Organic matter, B. Bacterial content, C. Anaerobic bacteria, D. Chemicals', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Organic matter", 'role': 'assistant'}]