What is NOT a primary function of the skeletal system?

The skeletal system primarily serves three main functions: providing structural support to the body, facilitating movement, and storing minerals while producing blood cells. While the skeletal system does contribute to body protection, especially for vital organs (like the skull protecting the brain or ribs safeguarding the heart and lungs), the term "protective covering on body surfaces" is more accurately associated with other systems, particularly the integumentary system, which includes the skin.

In this context, a protective covering refers to the skin, which serves as a barrier against environmental hazards, pathogens, and physical injuries, rather than the bones and structures of the skeletal system. Hence, the function of providing a protective covering on body surfaces falls outside the primary role of the skeletal system, making it the correct answer for what is not a primary function of the skeletal system.