This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and health, Subject name: Social & Preventive Medicine
[{'content': 'Sandfly can fly upto - \nSelect and explain. \nA. 50 yards, B. 100 yards, C. 200 yards, D. 300 yards', 'role': 'user'}, {'content': "Answer: A \nExplanation: Sandflies Sansflies are troublesome nocturnal pests. They are incapable of flying over long distances. They merely hop about from one place to another. Sandflies are generally confined to within 50 yards. REFERENCE: PARK'S TEXTBOOK OF PREVENTIVE AND SOCIAL MEDICINE, 25TH EDITION, PG NO. 835", 'role': 'assistant'}]