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': 'Spot map was devised by ? \nSelect and explain. \nA. Louis pasteur, B. Ronald Ross, C. David Moley, D. John snow', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. is 'd' i.e., John snow John Snow (1813-1858) found the link between cholera and contaminated drinking water in 1854, using spot map.", 'role': 'assistant'}]