题目内容：
根据以下材料，回答题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 51______ people frequently. But these fish perform a 52______ service for earth's waters and for human beings. Yet business and sport fishing are threatening their 53______ Some sharks are at risk of disappearing from 54______
Warm weather may influence both fish and shark activity. Many fish swim near coastal areas 55______ their warm waters. Experts say sharks may follow the fish into the same areas,56______ people also swim. In fact, most sharks do not purposely charge at or bite humans. They are thought to mistake a person 57______ 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 58______ 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 smell4. It can find small amounts of substances in water, such as blood, body liquids and 59______ produced by animals. These powerful 60______ help sharks find their food. Sharks eat fish, any 61______ sharks, and plants that live in the ocean.
Medical researchers want to learn more about the shark's body defense, and immune 62______ against disease. Researchers know that sharks 63______ quickly from injuries. They study the shark in hopes of finding a way to fight human disease.
Sharks are important for the world's 64______. They eat injured and diseased fish. Their hunting activities mean that the numbers of other fish in ocean waters do not become too 65______
This protects the plants and other forms of life that exist in the oceans.
回答(51)题 A．attack
B．meet
C．love
D．visit
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