If you are a typical ocean-goer, your chances of being killed by an unprovoked 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 (免疫的) 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 extracted (提取) from shark cartilage have killed cancerous tumors in laboratory animals, research that someday could help prolong your life,
Sharks are needed in the world’s ocean ecosystems (生态系统). 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.
55. Which statement best expresses the main idea of the article?
There are many different species of sharks, but only a few of them are dangerous to humans.
Sharks play an important role in the ocean ecosystem and they are a valuable resource for humans.
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