I think it is NAD, this ensures that the NAD can go back to glycolysis where it can again be reduced and go back through anaerobic respiration.
Everything in Earth's system can be placed into one of four major subsystems: land, water, living things, or air. These four subsystems are called “spheres.” Specifically, they are the lithosphere (land), hydrosphere (water), biosphere (living things), and atmosphere (air)...
I hope this helps you with biology...
---nila---
