This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diseases of orbit, Lids and lacrimal apparatus, Subject name: Ophthalmology
[{'content': 'Frequency of USG used in ophthalmics is \nSelect and explain. \nA. 8, B. 18, C. 15, D. 12', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ultrasonic frequency in the range of 10MHz are used for ophthalmic diagnosis Ref khurana 6/e', 'role': 'assistant'}]