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': 'Follow–up of cataract operations in national blindness control program is done by – \nSelect and explain. \nA. Active surveillance, B. Passive surveillance, C. Sentinel surveillance, D. Routine check-up', 'role': 'user'}, {'content': 'Answer: C \nExplanation: 25 sentinel surveillance units have been established in departments of ophthalmology and PSM in medical collages in India for assessment of -\nBeneficiary profiles.\nVisual outcomes based on cataract surgery records.\nFollow-up of operated cases. \xa0\nOcular morbity data.', 'role': 'assistant'}]