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': 'Smallest diameter of the eyeball is: \nSelect and explain. \nA. Veical, B. Horizontal, C. Anteroposterior, D. More than 24 mm', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Veical', 'role': 'assistant'}]