Which system consists of the skin, mucous membranes, hair, and nails?

The integumentary system is the correct choice because it is defined as the body's outer covering that includes the skin, mucous membranes, hair, and nails. This system serves multiple critical functions, such as protecting the body from external damage, regulating temperature, and allowing sensory perception. The skin acts as the primary barrier, while hair and nails serve protective and sensory roles.

The nervous system, on the other hand, is responsible for transmitting signals between different parts of the body and processing information. The skeletal system provides structural support and protection for the body’s organs, consisting mainly of bones and cartilage. Meanwhile, the muscular system is involved in movement and stability through its muscles. Each of these systems has distinct roles and components, making the integumentary system uniquely identifiable by the elements it encompasses.