This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Concept of health and disease, Subject name: Social & Preventive Medicine
[{'content': 'Smallpox vaccine was introduced by \nSelect and explain. \nA. Paul Ehrlich, B. Robe Koch, C. Louis Pasteur, D. Edward Jenner', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Edward Jenner discovered smallpox vaccine in1796', 'role': 'assistant'}]