Answer:
The correct answer is "reduce NAD+ to NADH, which then delivers them to the electron transport chain".
Step-by-step explanation:
During cellular respiration, high-energy electrons are released from glucose and they move gradually through the electron transport chain towards oxygen. Most of these high-energy electrons are used to reduce NAD+ to NADH, which then delivers them to the electron transport chain. The reduction of NAD+ is the first step of the electron transport chain, which is transported from NADH and FADH2 to molecular oxygen.