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': 'Yellow fever vaccination starts protection after how many days of injection - \nSelect and explain. \nA. 5 days, B. 10 days, C. 15 days, D. 20 days', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]