NaD is a coenzyme for many enzymes involved in redox reactio

NaD^+ is a coenzyme for many enzymes involved in redox reaction. This means that NAD^+ has an active site. All enzymes involved in redox reactions bind NAD^+ Enzymes that use NAD^+ as coenzyme will not function property if NAO^+ is not available. NAD^+ is ana inhibitor of many enzymes involved in redox chemistry.

Solution

most probably option C.

A. enzymes have the active sites. coenzymes, in general, donot have active sites. They have only binding sites.

B. all enzymes donot need NAD as a coenzyme. even FAD and NADP act a coenzyme for some redox reactions.

C. enzymes that generally use NAD have binding site specific to NAD. therefore they may not function properly in its absence.

D. NAD is not an inhibitor of enzymes.