Sharks Perform aService for Earth's Waters

It is hard to getpeople 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 andfor human beings .Yet business and sport fishing are threateningtheir______(53).Some sharks are at______(54)of disappearing from earth.

Warm weather mayinfluence 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 orbite humans.

They are thought tomistake a person______(57)a sea animal,such as a seal or sea lion.That is whypeople 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 colorsand shiny jewelry may cause sharks to attack.

A shark has anextremely good sense of smell.It can find small amounts of substances inwater,such as blood,body liquids and______(59)produced by animals.These

powerful______(60)help sharks find their food.Sharks eat fish,any______(61)sharks,andplants that live in the ocean.

Medical researcherswant to learn more about the shark's body defense and immune systems______(62)disease.Researchers know that sharks______(63)quickly from

injuries.They studythe shark in hopes of finding a way to fight human disease.

Sharks are importantfor the world's______(64).They eat injured and diseased fish. Their huntingactivities mean that the numbers of other fish in ocean waters do not become

too ______(65).Thisprotects the plants and other forms of life that exist in the oceans.52._________

A.. terrible

B. eatable

C. valuable

D. possible