Which statement about natural background radiation is correct?

• A. It originates from terrestrial materials.
• B. It originates from cosmic sources and terrestrial materials.
• C. It originates from medical procedures.
• D. It originates from nuclear fallout.

Answer: (B)

Natural background radiation comes from two main sources: cosmic rays from outer space and naturally occurring radioactive materials in the Earth's crust. This combination forms the baseline exposure people receive and can vary with altitude and local geology (more cosmic radiation at higher altitudes, more rock-derived radiation in certain areas). The statement that natural background radiation originates from cosmic sources and terrestrial materials is the best description because it includes both major natural contributors. Medical procedures and nuclear fallout are human-made sources of radiation, not part of natural background.