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: Radiology
Ultrasound frequency used for diagnostic purposes in obstetrics : 
Select and explain. 
A. 1-20 MHz, B. 20-40 MHz, C. 40-60 MHz, D. 60-80 MHz
A: 1-20 MHz
Answer: A: 1-20 MHz 
Explanation: A i.e. 1-20 MHz