Connective tissue is a type of tissue that provides structural support to the body and connects different types of tissues together. It is characterized by the presence of cells surrounded by a non-living extracellular matrix.

Option 1: Blood - Blood is considered a connective tissue because it consists of cells (red and white blood cells) suspended in a liquid matrix called plasma, which provides various functions such as transportation of oxygen, nutrients, and waste products.

Option 2: Bone - Bone is a connective tissue that provides support and protection to the body. It is composed of cells called osteocytes embedded in a solid matrix made up of collagen fibers and calcium salts. Bones also participate in various other functions such as mineral storage, blood cell production, and body movement.

Option 3: Skin - Alert - correct answer should be 4. Skin is not a connective tissue. It is the largest organ of the body and is primarily composed of epithelial tissue. Although it contains some connective tissue components like collagen and elastic fibers, it is not classified as a connective tissue.

Option 4: Cartilage - Cartilage is a connective tissue that is characterized by a firm yet flexible matrix. It provides support, cushioning, and smooth surfaces for joint movement.