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 an aphakic eye the anterior focal point from the anterior surface of cornea is about: \nSelect and explain. \nA. 15 mm, B. 21 mm, C. 23 mm, D. 31 mm', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. 23 mm', 'role': 'assistant'}]