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': 'Secondary attack rate of chickenpox ? \nSelect and explain. \nA. 70%, B. 90%, C. 65%, D. 80%', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is `b' i.e., 9%", 'role': 'assistant'}]