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Sharks Perform a Service for Earths Waters It is hard to get people to think of sharks as anything but a deadly enemy1: They are thought to____1____people frequently. But these fish2 perform a____2____service for earths 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 sharks 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. | 
