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
The ultrasonic sound waves employed in ultrasound machine for medical sonography have the frequency of - 
Select and explain. 
A. 2 – 20 MHz, B. Less than 1 MHz, C. 20 – 20, 000 Hz, D. Greater than 100 MHz
A: 2 – 20 MHz
Answer: A: 2 – 20 MHz 
Explanation: None