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': 'For biometric studies of the eyeball best pulse echo technique on ultrasonography is: \nSelect and explain. \nA. A Scan, B. B Scan, C. C Scan, D. All of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. A Scan', 'role': 'assistant'}]