Question

type of organic molecule an enzyme is

Explanation:

Enzymes are biological catalysts, but the question asks for the type of organic molecule. Enzymes (except for some RNA - based ribozymes, but most are proteins) are primarily proteins. Substrate is the molecule an enzyme acts on, catalyst is the role of the enzyme, and "Lock & Key" is a model of enzyme - substrate interaction, not the molecule type.

Answer:

C. Protein (assuming the options are labeled as A. Substrate, B. Catalyst, C. Protein, D. Lock & Key)