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
Which is not mutagenic? 
Select and explain. 
A. X-rays, B. UV rays, C. Ultrasound, D. Beta rays
C: Ultrasound
Answer: C: Ultrasound 
Explanation: Ans. Ultrasound