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': 'Which events occurred before 1900 AD \nSelect and explain. \nA. Establishment of seat of social medicine at Oxford, B. Use of BCG vaccine, C. Epidemiological work on cholera by John Snow, D. Work on scurvy by james Lind', 'role': 'user'}, {'content': 'Answer: C \nExplanation: An english epidemiologist John Snow studied the epidemiology of cholera in London from 1848-1854 and established the role of polluted drinking water in spread of cholera.', 'role': 'assistant'}]