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': 'The infectivity of chickenpox lasts for \nSelect and explain. \nA. Till the last scab falls off, B. 6 days after onset of rash, C. 3 days after onset of rash, D. Till the fever subsides', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Period of communicability:\n– Chickenpox: 1 – 2 days before to 4 – 5 days after appearance of rash\n– Measles: 4 days before to 5 days after appearance of rash\n– Diphtheria: 14 – 28 days from disease onset\n– Poliomyelitis: 7 – 10 days before and after onset of symptoms', 'role': 'assistant'}]