What is a primary source of natural background radiation?

The correct choice identifies cosmic radiation and terrestrial radiation as primary sources of natural background radiation. Cosmic radiation originates from outer space, consisting of high-energy particles from the sun and other celestial sources that penetrate the earth's atmosphere. Terrestrial radiation comes from radioactive materials found naturally in the Earth, such as uranium, thorium, and radon, which decay and release radiation as part of their natural processes.

Both cosmic and terrestrial radiation contribute significantly to the overall exposure individuals receive from natural sources, making them essential components of the natural background radiation experienced in everyday life. This exposure varies depending on geographic location, altitude, and local geology, reflecting the nature and density of natural radioactive materials in the environment.

In contrast, the other options presented relate to specific types of radiation exposure that are not natural background sources. Artificial radioactive waste is produced from human activities, such as nuclear power generation, while radiation from medical procedures and industrial sources involves artificial applications that are not part of the natural environment. Thus, option B stands out as the only choice representing a natural source of radiation.