This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
[{'content': "'Ring vaccination' is \nSelect and explain. \nA. Given by a ring shaped machine, B. Given to produce a ring lesion, C. Given around 100 yards of a case detected, D. Given around a mile of a case", 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ring vaccination is a strategy to inhibit the spread of disease by vaccinating only those who are most likely to be infected.', 'role': 'assistant'}]