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': 'Vaccine of yellow fever is \nSelect and explain. \nA. 17D, B. 5D, C. 4D, D. 2D', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]