Cartilaginous fishes are characterized by skeletons made of cartilage. Which best completes this statement?

• A. Bone
• B. Cartilage
• C. Muscle
• D. Nerve tissue

Answer: (B)

The basic idea here is the material that forms the skeleton in different vertebrates. Cartilaginous fishes have an endoskeleton made of cartilage, a flexible connective tissue that provides support without the rigidity of bone. This lighter, more pliable skeleton suits their need for agile swimming and buoyancy in water. Bone, by contrast, is characteristic of bony fishes and many terrestrial vertebrates, offering rigid support and mineral storage. Muscle tissue and nerve tissue are essential for movement and signaling, not for forming the skeletal framework. So cartilage is the best completion because it directly describes the skeletal material unique to cartilaginous fishes.