Where does radioactivity come from?

a the decay of certain atomic nuclei

b the atom losing electrons

c radioactive material

d U-238

C. radioactive material

Explanation:

This exposure primarily comes from cosmic rays, radioactive material in the earth (such as uranium-238), ingestion of naturally occurring radionuclides in food (such as potassium - 40), and inhalation of radon gas. In the United States, the average background radiation dose is 300 mrem/yr.