Which of the Following Best Describes a Natural Radioactive Decay

Which of the following best describes a natural radioactive decay series?

A) Change of one element to another by nuclear bombardment
B) A chain reaction, in which a nuclear product of one reaction becomes a nuclear reactant in the next step
C) The combination of two small nuclei to form a larger nucleus
D) A list of a series of reactions that illustrate how a radioactive element disintegrates into a stable isotope
E) A nuclear equation for a natural radioactive decay, showing the alpha and beta particles written as a series rather than with coefficients