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': 'Anteroposterior diameter of normal adult eyeball is: \nSelect and explain. \nA. 25 mm, B. 24 mm, C. 23.5 mm, D. 23 mm', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. 24 mm', 'role': 'assistant'}]