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 frequendy. But these fish perform a【C2】______service for earth’s watersand for human beings. Yet business and sport fishing are threatening their【C3】______. Somesharks are at【C4】______of disappearing from earth.
    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. Thatis 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 plantsthat live in the ocean.
    Medical researchers want to learn more about the shark’s body defense and immune systems【C12】______ disease.Researchers know that sharks【C13】______quickly from injuries. Theystudy 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. Theirhunting 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.
【C9】

选项 A、sciences
B、mathematics
C、chemicals
D、physics

答案C

解析 本段第一、二句是说,鲨鱼的嗅觉特别灵敏,能嗅到海水中存在的极为微量的气味。作者举了三个物质:血、体液和化学品。空格要填入表示物质的名词。四个选项中唯一表达物质的词是chemicals(化学品)。所以chemicals是答案,而其他三个选项与学科有关,脱离了上下文的意思,不是本题的答案。
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