Which of the following is typically the largest source of radiation exposure for humans?

Question

artificial radiation sources
atmospheric radon
cosmic rays
terrestrial radiation

Answer 1

Terrestrial radiation - especially in parts of South America.

Answer 2

It depends whether you mean largest in quantity (over the lifespan of an individual) or most concentrated. Probably terrestrial radiation is the greatest in total quantity over years. Even beach sand contains a small amount of the heavy mineral monzonite, which contains radioactive thorium. Old mineral sands dumps can emit surprisingly high levels of radiation.
In terms of most concentrated (and hence, most dangerous), artificial sources would probably be then greatest, but few are exosed to them, and generally for a short time (which, nevertheless might prove fatal).

Answer 3

Sunlight is the largest source.