Which system includes hair, skin, and nails?

The integumentary system is the appropriate choice because it is specifically responsible for protecting the body and maintaining homeostasis. This system includes the skin, hair, nails, and associated glands, all of which play vital roles in the protection against pathogens, regulation of temperature, and the retention of body fluids.

Skin is the largest organ of the body and serves as a barrier to prevent infection and dehydration. Hair and nails also contribute to protection – hair can help to regulate body temperature and provides a barrier to foreign particles, while nails protect the digital tips from injury and assist in various functions like picking up objects.

The other systems mentioned do not incorporate these structures. The circulatory system focuses on the transportation of blood and nutrients throughout the body, the musculoskeletal system pertains to the bones and muscles that support movement and structure, and the nervous system is involved in transmitting signals between different parts of the body for coordination and response. Thus, the integumentary system is uniquely defined by its components: hair, skin, and nails.