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　　A small piece of fish each day may keep the heart doctor away. That's the finding of an extensive study of Dutch men in which deaths from heart disease were more than 50 percent lower among those who consumed at least an ounce of salt water fish per day than those who never ate fish.

　　The Dutch research is one of three human studies that give strong scientific backing to the long-held belief that eating fish can provide health benefits, particularly to the heart.

　　Heart disease is the number-one killer¹ in the United States, with more than 550,000 deaths occurring from heart attacks each year. But researchers previously² have noticed that the incidence ( 发生率) of heart disease is lower in cultures that consume more fish than Americans do. There are fewer heart disease deaths, for example, among the Eskimos of Greenland, who consume about 14 ounces of fish a day, and among the Japanese, whose daily fish consumption averages more than 3 ounces.

　　For 20 years, the Dutch study followed 852 middle-aged³ men, 20 percent of whom ate no fish.

　　At the start of the study, the average fish consumption was about two-thirds of an ounce each day with more men eating lean (瘦的) fish than fatty fish.

　　During the next two decades, 78 of the men died from heart disease. The fewest deaths were among the group who regularly ate fish, even at levels far lower than those of the Japanese or Eskimos. This relationship was true regardless of other factors such as age, high blood pressure, or blood cholesterol⁴ ( 胆固醇) levels.

　　51. Which of the following is NOT true according to the passage?

　　[A] The Dutch research has proved that eating fish can help to prevent heart disease.

　　[ B] Heart doctors won't call your house so long as you keep eating fish each day.

　　[C] Among all the diseases heart disease is the most dangerous in America.

　　[D] There is a low incidence of heart disease in such countries as Japan and Greenland.

　　52. The phrase "this relationship" (in Line 3, Para. 5) refers to the connection between

　　_________ and the incidence of heart disease.

　　[A] the amount offish eaten     [B] regular fish-eating

　　[ C ] the kind of fish eaten       [ D ] people of different regions

　　53. The passage is mainly about _________.

　　[ A ] the high incidence of heart disease in some countries

　　[ B ] the effect of fish eating on people's health

　　[ C] the changes in people's diet

　　[D] the daily fish consumption of people in different cultures

　　54. Why is heart disease the most dangerous killer in the United States?

　　[A] Because American people drink too much spirits.

　　[B] Because there are a great number of fat people there.

　　[ C ] The author doesn't give a definite answer.

　　[D] Because American people eat too much fatty fish.

　　55. How many lives could probably be saved each year in the United States by eating fifth according to the Dutch study?

　　[A] 550,000.                 [B] 275,000.

　　[C] 110,000.                  [D] 852.