题目内容：
请根据短文内容，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__________(1) people frequently. But these fish perform a__________ (2) service for earth's waters and for human beings. Yet business and sport fishing3 are threatening their__________(3).
Some sharks are at risk of disappearing from __________ (4).
Warm weather may influence both fish and shark activity. Many fish swim near coastal areas__________ (5) their warm waters. Experts say sharks may follow the fish into the same areas,__________ (6) people also swim. In fact, most sharks do not purposely charge at or bite humans.
They are thought to mistake a person __________ (7) 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__________(8) 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 __________(9) produced by animals. These powerful__________ (10) help sharks find their food. Sharks eat fish, any__________(11) sharks, and plants that live in the ocean.
Medical researchers want to learn more about the shark's body defense, and immune__________(12) against disease. Researchers know that sharks __________ (13) quickly from injuries. They study the shark in hopes of finding a way to fight human disease.
Sharks are important for the world's __________ (14). They eat injured and diseased fish.
Their hunting activities mean that the numbers of other fish in ocean waters do not become too__________(15). This protects the plants and other forms of life that exist in the oceans.
__________ A．attack
B．meet
C．love
D．visit
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