Which of the following is not a function of protein?
a. cells communicate
b. serving as enzymes
c. insulating the body
d. giving cells structure

C. Insulating the body

Insulating the body is not a function of a protein.

Lipids are macromolecules which provide insulation. 
A macromolecule is a large molecule. There are four groups of macromolecules: carbohydrates, proteins, nucleic acids and lipids. Lipids consist of glycerol and fatty acids and are constructed from fats, oils, waxes, phospholipids and steroids. A lipid's function is to insulate the body and provide warmth in cold conditions. It can be concluded that a person with very little body fat gets very cold easily and a person with a lot of body fat gets very warm very quickly.