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': 'Vector control for yellow fever around an airpo is done upto a distance of- \nSelect and explain. \nA. 400m, B. 200m, C. 500m, D. 100m', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., 400 m o Airpos and seapos are kept free from the breading of insect vectors over an area extending at least 400 meters around their peripeters.", 'role': 'assistant'}]