What Distinguishes Natural Radioactivity from Induced Radioactivity Produced by Bombardment

What distinguishes natural radioactivity from induced radioactivity produced by bombardment reactions?

A) Gamma rays are not emitted in natural radioactivity
B) Gamma rays are not emitted in induced radioactivity
C) Induced radioactivity produces radioactive elements not found in nature
D) Induced radioactivity is still a theoretical concept; natural radioactivity actually occurs
E) When naturally radioactive substances decay, they emit natural radiation, but when induced radioactive substances decay, they emit artificial radiation