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

The integumentary system is the correct answer because it encompasses all the components mentioned in the question: the skin, mucous membranes, hair, and nails. This system serves several critical functions, including protection against environmental hazards, regulation of body temperature, and sensory perception. The skin acts as a barrier to pathogens and physical injuries, while hair can provide insulation and protection as well. The mucous membranes line various cavities and structures in the body, playing a role in moisture retention and protection against pathogens.

The other systems listed do not include skin or the other components mentioned. The skeletal system's primary focus is on supporting the body structure through bones and cartilage, while the nervous system is responsible for processing sensory information and coordinating responses through neurons. The endocrine system, on the other hand, is involved in hormone production and regulation, managing processes such as metabolism and growth, but does not consist of the components specified in the question. Thus, the integumentary system clearly integrates all the structures identified.