[不定项选择题]共用题干 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 ______(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. 55._________
A.because
B.since
C.because of
D.by reason that