题目内容：
根据下面材料，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____ 1 ____people frequently. But these fish perform a ____2____ service for earth's waters and for human beings. Yet business and sport fishing ____3____ are threatening their3 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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