Read the passage then choose the best answer for the following questions by marking the corresponding letter: A, B, C, or D from 7 to 11.

Most people are afraid of sharks, but they usually do not know much about them. For example, there are about 350 species of sharks that live in oceans over the world. All of the sharks are carnivores, but most of them don't attack people. Some sharks are very small – the smallest shark is about 6 inches long - about as long as your hand. But some sharks are very large. The largest species of sharks may be 60 feet long and weigh 15 tons. Unlike many other kinds of fish, sharks do not have bone. Their bodies are made up of a kind of tough white flexible material (called cartilage). Sharks do not have ears. However, they 'hear' sounds and movements in the wade. Any sound or movement makes the water vibrates. Sharks can feel these vibrations and they help the sharks find food. Sharks use their large eyes to find food, too. Most sharks see best in low light. They often hunt for food at dawn in the evening, or in the middle of the night.

Nowadays scientists want to learn more about sharks for several reasons. For example, cancer is common in many animals, including, people. However, it is rare in sharks. Scientists want to find out why sharks almost never get cancer. Maybe this information can help people prevent cancer too.