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': 'The anterior focal length of the schematic eye is: \nSelect and explain. \nA. 15.7 mm, B. 17.2 mm, C. 13 mm, D. None of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. 17.2 mm', 'role': 'assistant'}]