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': 'What is the recommended Aedes aegypti index value to ensure freedom from yellow fever? \nSelect and explain. \nA. <0.1 %, B. <1%, C. <0.5%, D. <5%', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Aedes aegypti index is used for surveillance of Aedes mosquitoes by WHO. The index should be< 1% in towns and sea pos in endemic areas to ensure freedom from yellow fever. Ref: Park 21st edition, page 259.', 'role': 'assistant'}]