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.
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.
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
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
65. A weak B little C few D great
答案：
51 A 52B 53 C 54 D 55 C
56 D 57 B 58 A 59 C 60 B
61 D 62 A 63 A 64 B 65 D
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