The correct option is A Proteins
Enzymes are proteins which play a significant role in catalytic reactions as the catalysts in the living system. An enzyme consists of a protein part (apoenzyme) and non-protein part (cofactor). The apoenzyme and cofactor together are called holoenzymes.
There are three kinds of cofactors - prosthetic groups, coenzymes and metal ions.
The non-protein but organic part which is permanently attached to the enzyme is called the prosthetic group.
The coenzymes are transient organic groups which are not attached to the apoenzyme permanently like the prosthetic group.
Metal ions are the inorganic cofactors.