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': 'WHO definition of blindness is a visual acuity in the better eye equal to or less than: \nSelect and explain. \nA. Mar-60, B. Apr-60, C. May-60, D. Jun-60', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. 4/60', 'role': 'assistant'}]