Answer the following question given this paragraph: 

Gamma rays are the most energetic of all electromagnetic waves. They can pass through most materials, including bones and teeth. Nonetheless, even these waves are useful. For example, they can be used to treat cancer. A medical device sends gamma rays the site of the cancer, and the rays destroy the cancerous cells. If you want to learn more about gamma rays, watch the video at the URL below.


Q: What are the most energetic of all electromagnetic waves, which can be used to treat cancer?

 Choices:

- ultraviolet

- infrared

- X-ray

- gamma rays

A:
gamma rays
