In oxidative phosphorylation, what is the primary function of NADH and FADH$2_{}$?

• A. They transport oxygen from the lungs to mitochondria to serve as the final electron acceptor.
• B. They act as terminal electron acceptors by combining with electrons and protons to form water at Complex IV.
• C. They donate high-energy electrons to the electron transport chain (e.g., Complex I for NADH and Complex II for FADH$2_{}$), helping drive proton pumping and ATP synthesis.
• D. They directly catalyze the phosphorylation of ADP to ATP by transferring a phosphate group to ADP.

Answer: (C)