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': 'The distance from airpo or seapo which has to be free from mosquitoes is - \nSelect and explain. \nA. 400 m, B. 500 m, C. 1 km, D. 100m', 'role': 'user'}, {'content': "Answer: A \nExplanation: - The aircraft and ships arriving from endemic areas are subjected to aerosol spraying with prescribed insecticides on arrival for destruction of insect vectors. -The distance from airpo or seapo which has to be free from mosquitoes is 400 meters. Reference : Park's textbook of preventive and social medicine, 23rd edition pg no:284", 'role': 'assistant'}]