Which of the following is NOT considered connective tissue?

Skin is primarily classified as an organ that consists of multiple tissue types, including epithelial tissue, connective tissue, and muscle tissue. While it does have connective tissue components, such as the dermis, which supports and houses blood vessels, hair follicles, and other structures, skin itself is not solely categorized as connective tissue.

In contrast, cartilage, blood, and bone are all classified as types of connective tissues. Cartilage serves as a flexible support structure, blood has a unique role as a fluid connective tissue that transports nutrients and waste, and bone provides structural support and protection to various organs. Therefore, skin is the only option that does not fit neatly into the connective tissue category.