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 of the following is not a killed vaccine ? \nSelect and explain. \nA. Polio, B. HBV, C. HAV, D. Yellow fever vaccine', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. is 'd' i.e., Yellow fever vaccine Yellow fever vaccine is a killed vaccine.", 'role': 'assistant'}]