The Driving Force Which Provides the Energy for Synthesis of ATP

The driving force which provides the energy for synthesis of ATP in the fourth stage of metabolism is the

A) exergonic conversion of ADP to ATP.
B) energy difference between reduced carbon atoms and oxidized carbon atoms.
C) concentration gradient of hydrogen ions between the two sides of the inner mitochondrial membrane.
D) concentration difference in oxygen between the cell and the intercellular fluid.
E) none of the above