This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nuclear medicine, Subject name: Radiology
Killing of Thyroid Cancer cells By I-131 is mainly by 
Select and explain. 
A. Alpha Rays, B. X rays, C. Beta Rays, D. Gamma Rays
C: Beta Rays
Answer: C: Beta Rays 
Explanation: *I-131 produces both Gamma and Beta Rays, but killing of thyroid cancer is mainly done by Beta Rays.