Final answer:
A shark's skeleton is made of cartilage, which is a tough and flexible type of connective tissue.
Step-by-step explanation:
A shark's skeleton is made of cartilage, which is a tough and flexible type of connective tissue. Cartilage contains a protein called collagen and provides support and structure to the shark's body. Unlike bone, cartilage is lighter and more flexible, which allows sharks to swim more efficiently in water.