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': 'First reliable census was conducted in: \nSelect and explain. \nA. 1881, B. 1951, C. 1981, D. 2001', 'role': 'user'}, {'content': 'Answer: A \nExplanation: 1881', 'role': 'assistant'}]