Answer: b. they accept a hydrogen molecule
Explanation:
NAD +: Nicotinamide Adenine Dinucleotide- Coenzyme that assists biological reactions by absorbing hydrogen atoms removed from the substrate. Its reduced form NADH or NADH2 contains more energy, which can be used to generate ATP in later reactions. Other examples of coenzymes used in the energy metabolism: FAD (Flavin Adenine Dinucleotide) and its reduced form FADH2