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
Frequency of USG used in ophthalmics is 
Select and explain. 
A. 8, B. 18, C. 15, D. 12
A: 8
Answer: A: 8 
Explanation: Ultrasonic frequency in the range of 10MHz are used for ophthalmic diagnosis Ref khurana 6/e