Sharks have lived in the oceans for over 450 million years, long before dinosaurs appeared. There are now about 360 species of sharks, whose size, behavior, and other characteristics differ widely. Every year, we catch and kill over 100 million sharks, mostly for food and for their fins. Dried shark fins are used to make shark fin soup, which sells for as much as $50 a bowl in fine Hong Kong restaurants. Other sharks are killed for sport and out of fear. Sharks are vulnerable(易受伤的) to overfishing because it takes most species 10 to 15 years to begin reproducing and they produce only a few offspring（后代）. Influenced by movies and popular novels, most people see sharks as people-eating monsters. This is far from the truth. Every year, a few types of shark injure about 100 people worldwide and kill about 25. Most attacks are by great white sharks, which often feed on sea lions and other marine（海洋的） mammals. They sometimes mistake human swimmers for their normal prey, especially if they are wearing black wet suits. If you are a typical ocean-goer, your chances of being killed by an unprovoked（非受挑衅而发生的）attack by a shark are about 1 in 100 million. You are more likely to be killed by a pig than a shark and thousands of times more likely to get killed when you drive a car. Sharks help save human lives. In addition to providing people with food, they are helping us learn how to fight cancer, bacteria, and viruses. Sharks are very healthy and have aging processes similar to ours. Their highly effective immune system allows wounds to heal quickly without becoming infected, and their blood is being studied in connection with AIDS research. Sharks are among the few animals in the world that almost never get cancer and eye cataracts（白内障）. Understanding why can help us improve human health. Chemicals taken from shark cartilage（软骨）have killed cancerous tumors in laboratory animals, research that someday could help prolong your life. Sharks are needed in the world’s ocean ecosystems. Although they don’t need us, we need them. We are much more dangerous to sharks than they are to us. For every shark that bites a person, we kill one million sharks. 小题1:Which of the following is NOT a reason why people kill sharks?
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