Which one of the following would be correctly classified as a protein? answer cellulose enzymes starch cholesterol

The answer to this question is Enzymes.

An enzyme is defined as a protein catalyst. Many enzymes consist of a protein, the apoenzyme,  and a non protein component known as a cofactor required for catalytic activity. The complete enzyme consisting of  the apoenzyme and its cofactor is called the holoenzyme. 

Cellulose is a polysaccharide made up of glucose units.

Cholesterol is an organic compound made of lipids with a rather unique structure consisting of hydrocarbons.

Starch is polysaccharide composed of amylose and amylopectin.