This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Optics and Errors of Refraction, Subject name: Ophthalmology
[{'content': "A person came to eye OPD for routine eye check u. On snellen's cha he was found to read 6/6. At what distance he should be able to read 6/24 \nSelect and explain. \nA. 36 m, B. 24 m, C. 6 m, D. 1 m", 'role': 'user'}, {'content': "Answer: B \nExplanation: What does 6/6 mean in Snellen's cha * It means that the patient with or without glasses can see the letter at a distance of 6 m which a person normally should have been seeing at 6 m Now you would understand it by next example * 6/12 means a letter which a normal patient should be seeing at 12 metre , this patient can see only when he is nearer, that means 6 metre from Target * 6/24 means that a normal patient should be seeing at 24 metre, but this patient has to be much closer that means 6 metre * This also means that the letter written at 6/24 is big enough that 6/6 vision person can read it at even 24 metre", 'role': 'assistant'}]