This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Concept of Control, Subject name: Social & Preventive Medicine
[{'content': 'Polio vaccine is which type of prevention: \nSelect and explain. \nA. Primary, B. Secondary, C. Tertiary, D. Primordial', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (a) PrimaryRef.: K. Park 23rd ed. 141, 370-74', 'role': 'assistant'}]