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': 'When did WHO declare world free of small pox? \nSelect and explain. \nA. 1965, B. 1970, C. 1975, D. 1980', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Small pox was declared eradicated in 198i0 by WHO. India was declared free of small pox in 1977. Ref: Park 21st edition, page 132 Chapter: Epidemiology in communicable diseases.', 'role': 'assistant'}]