Answer:
Explanation:
Background radiation is a measure of the ionizing radiation present in the environment. The most common source of this is cosmic radiation, which is formed by high energy sub-particles, which almost at light speed. All these particles come from the Sun and other stars, even from other galaxies.
In addition, another common source is the environmental radioactivity, which is produced by radioactive materials, some naturals, other by humans.
Therefore, the answer that best fit is cosmic radiation.
