This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Communicable diseases, Subject name: Social & Preventive Medicine
[{'content': 'In an area not covered by measles immunization, the attack rate of measles is - \nSelect and explain. \nA. 70%, B. 80%, C. 90%, D. 100%', 'role': 'user'}, {'content': 'Answer: C \nExplanation: when the disease is introduced to a virgin community more than 90 % of that community will be infected (park,edition 23,page 146)', 'role': 'assistant'}]