Which body system includes the skin, hair, and nails?

The integumentary system is the correct choice because it encompasses the skin, hair, nails, and associated glands. This system plays a crucial role in protecting the body from external damage, regulating temperature, and allowing sensory perception. The skin acts as a barrier against pathogens and helps to maintain hydration, while hair can provide protection from UV radiation and help with temperature regulation. Nails also serve to protect the sensitive tips of fingers and toes.

In contrast, the endocrine system primarily consists of glands that secrete hormones to regulate bodily functions, the muscular system is focused on movement and stability through muscles, and the nervous system facilitates communication throughout the body via nerves and the brain. Understanding these distinctions clarifies why the integumentary system specifically includes the mentioned components.