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.
【C5】

选项 A、because
B、since
C、because of
D、by reason that

答案C

解析 四个选项的意思都是因为,但是从用法上分析,because,since和byreason that之后要接句子,because of之后接名词或名词短语。their warm waters是名词短语,所以要选用because of。故C为正确答案。
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