The correct option is A Collagen
Cartilage is the flexible connective tissue that is found in many areas and is not as hard as bone but is stiffer and less flexible than muscles.
Cartilage is composed of specialized cells called chondrocytes that produce extracellular matrix composed of collagen fibers and abundant ground substance, which is rich in proteoglycans and elastin fibers.
Thus, the correct answer is the option (A), 'Collagen'.