Final answer:
Catabolic reactions involve the breakdown of larger molecules, while anabolic reactions involve the synthesis of larger molecules.
Step-by-step explanation:
In metabolism, catabolic reactions involve the breakdown of larger molecules into smaller molecules or atoms, while anabolic reactions involve the synthesis of larger molecules from smaller ones. The oxidation of NADH is associated with catabolic reactions, as it involves the release of energy. On the other hand, the reduction of NAD is associated with anabolic reactions, as it represents the formation of larger molecules. Therefore, the associations are:
a) Reduction of NAD - Anabolic
b) Makes covalent bonds - Both
c) Oxidation of NADH - Catabolic
d) Biosynthetic reaction - Anabolic