Which statement BEST describes the relationship between adenosine diphosphate (ADP) and adenosine triphosphate (ATP)? A. With an input of energy, ADP rearranges to become ATP. B. Without any energy change, ADP rearranges to become ATP. C. With an input of energy, ADP combines with a phosphate group to become ATP. D. With a release of energy, ADP combines with a phosphate group to become ATP.