The direct energy source that drives ATP synthesis during respiratory oxidative phosphorylation in eukaryotic cells is

A) oxidation of glucose to CO₂ and water.
B) the thermodynamically favorable flow of electrons from NADH to the mitochondrial electron transport carriers.
C) the final transfer of electrons to oxygen.
D) the proton-motive force across the inner mitochondrial membrane.
E) the thermodynamically favorable transfer of phosphate from glycolysis and the citric acid cycle intermediate molecules of ADP.