Which system consists of the body’s outer covering?

It begins with cells, tissues, organs, organ system to organism. There are 11 organ systems that work collectively for an organism to function. Each organ is responsible for a different function and has its own structure. The organism system that consist of the body's outer covering is the integumentary system. It consist of skin, hair, nails, and endocrine glands; they are the protectors of the body. The environment such as UV rays are harmful and the skin, hair, nails, etc protect the body as needed. 

Ithink the answer is b, demographic transition theory.