Sharks Perform a Service for Earth’s Waters It is hard to get people to think of sharks as anything but a deadly enemy. They

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问题                 Sharks Perform a Service for Earth’s Waters
    It is hard to get people to think of sharks as anything but a deadly enemy. They are thought to【C1】______people frequently. But these fish perform a【C2】______service for earth’s waters and for human beings. Yet business and sport fishing are threatening their【C3】______Some sharks are at risk of disappearing from【C4】______.
    Warm weather may influence both fish and shark activity. Many fish swim near coastal areas【C5】______their warm waters. Experts say sharks may follow the fish into the same areas,【C6】______people also swim. In fact, most sharks do not purposely charge at or bite humans. They are thought to mistake a person【C7】______a sea animal, such as a seal or sea lion. That is why people should not swim in the ocean when the sun goes down or comes up. Those are the【C8】______when sharks are looking for food. Experts also say that bright colors and shiny jewelry may cause sharks to attack.
    A shark has an extremely good sense of smell. It can find small amounts of substances in water, such as blood, body liquids and【C9】______produced by animals. These powerful【C10】______help sharks find their food. Sharks eat fish, any【C11】______sharks, and plants that live in the ocean.
    Medical researchers want to learn more about the shark’s body defense and immune【C12】______against disease. Researchers know that sharks【C13】______quickly from injuries. They study the shark in hopes of finding a way to fight human disease.
    Sharks are important for the world’s【C14】______They eat injured and diseased fish.
    Their hunting activities mean that the numbers of other fish in ocean waters do not become too【C15】______. This protects the plants and other forms of life that exist in the oceans.
【C12】

选项 A、systems
B、processes
C、ideas
D、circles

答案A

解析 从上下文判断,医学研究人员想要更多了解鲨鱼的身体抗病system(系统)。idea:思想;work:工作;circle:周期。
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