Coenzymes are _______.
a. Types of apoenzymes
b. Proteins
c. Inorganic cofactors
d. Organic cofactors

Coenzymes are organic molecules that bind to enzymes and assist in catalyzing reactions by transferring chemical groups. They are not proteins themselves but work closely with enzymes to enhance their activity.

An apoenzyme is the protein portion of an enzyme without its cofactor, while a holoenzyme is the complete, active enzyme including its cofactor or coenzyme. Coenzymes are distinct from apoenzymes as they are non-protein organic molecules.

Cofactors are non-protein components required for enzyme activity. They can be inorganic ions like metal ions or organic molecules called coenzymes. Coenzymes often act as carriers for chemical groups during enzymatic reactions.