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': 'What is the period of infectivity in measles ? \nSelect and explain. \nA. From 7 days before to 7 days after the rash, B. From 3 days before to 5 days after the rash, C. From 9 days before to 12 days after the rash, D. From 5 days before to 9 days after the rash', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]