What tissue covers the body's external layer?

The body's external layer is covered by epithelial tissue, which serves as a protective barrier. This type of tissue consists of cells closely packed together, forming a continuous sheet. It plays several critical roles, including protection from environmental factors, absorption, secretion, and sensation. Epithelial tissue is found on the skin's surface as the epidermis, and it also lines various organs and cavities within the body, contributing to both physical protection and specialized functions.

Connective tissue provides support and structure to organs and tissues in the body but does not serve the primary function of covering surfaces. Muscle tissue is responsible for movement and contraction, while nervous tissue is involved in transmitting signals within the body. Therefore, the primary role of covering external surfaces is uniquely fulfilled by epithelial tissue, making it the correct choice in this context.