The best answer that describes the major group of macromolecules protecting Brett's car and how it is performing this task is:
C. Lipids are protecting his car because their nonpolar nature makes them insoluble in water.
In this context, the wax applied to the car is typically composed of lipids, which can form a hydrophobic (water-repelling) barrier. This helps protect the car's surface from water and other environmental elements.