[单项选择]Sharks
Sharks are amazing fish that have been around since long before the dinosaurs existed. They live in waters all over the world, in every ocean, and even in some rivers and lakes.
Sharks and Bony Fish
Unlike bony fish, sharks have no bones; their skeleton is made of cartilage(软骨), which is a tough, fibrous substance, not nearly as hard as bone. Cartilage, a strong fibrous(纤维的) substance, is softer than bone; our nose and ears are made of cartilage. Sharks also have no swim bladder (unlike bony fish).
Size
There are many different species of sharks that range in size from the size of a person’s hand to bigger than a bus. The whale shark is the largest fish in the world; the basking shark is the second largest fish. Fully-grown sharks range in size from 7 inches long (the Spined Pygmy shark), up to 50 feet long. Most sharks are intermediate in size, and are about the same size as people, 5 - 7 feet long. Half of the s
A. offensive
B. indifferent
C. interested
D. friendly