共用题干 Sharks Perform a Service for Earth's WatersIt 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______(54)of disappearing from earth.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 smell.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 systems ______(62)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. 57._________
A.to B.for C.like D.with正确答案B
