Which of the following statements is true? a. you are exposed to nuclear radiation every day. b. most of the nuclear radiation you are exposed to in the environment is man-made. c. naturally occurring nuclear radiation is called background decay. d. all natural radiation is at a level low enough to be saf

The correct option is A.
Radioactivity is part of the human existence on earth. It has been discovered that naturally occurring radioactive materials are present in the earth crust, in the food we eat, in the gases we exchange, etc. Humans are continuously exposed to radiations from both the earth and outside of the earth. The radiations that man is exposed to in the earth are of two types, natural and artificial radiations. Both can be harmful at diverse doses. Note that no scientific investigation has established it that natural radiations are quite harmless at their natural doses. 

Imma say go with a (: