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 risk of disappearing from_____ 54 .
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. 来源：考试大
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 _____62 against 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.
练习：
51. A attack B meet C love D visit
52. A terrible B eatable C valuable D possible
53. A source B existence C friends D fish
54. A Space B Sky C Land D Earth
55. A because B since C because of D by reason that
56. A whose B which C that D where
57. A to B for C like D with 采集者退散
58. A times B places C seas D oceans
59. A sciences B mathematics C chemicals D physics
60. A feelings B senses C touches D tastes
61. A those B these C another D other
62. A systems B processes C ideas D circles
63. A recover B reform C return D rely
64. A rivers B oceans C forests D mountains
55. A weak B little C few D great
答案：ACBDC DBACB DAABD