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: Ophthalmology
[{'content': "In the ninth revision of the international classification of diseases, 'Visual impairment' is a visual acuity in the better eye of: \nSelect and explain. \nA. 18-Jun, B. Jun-36, C. Jun-60, D. Mar-60", 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. 6/60', 'role': 'assistant'}]