What is the primary function of the rubber or plastic boot around a CV joint?

The primary function of the rubber or plastic boot around a CV joint is to keep out moisture and dirt. These boots serve as protective coverings that seal the joint and prevent contaminants from entering. If moisture or debris were to infiltrate the joint, it could lead to accelerated wear, corrosion, and ultimately failure of the CV joint. By maintaining a clean and dry environment, the boot ensures the longevity and proper functioning of the joint.

The other options do relate to aspects of vehicle performance or components, but they do not accurately describe the critical function of the CV joint boot. The primary task is focused on protection rather than enhancing strength, performance, or reducing noise directly. While the boot may indirectly contribute to minimizing noise by keeping the joint healthy, that is not its primary role.