[填空题]Eating fish and walnuts may help keep our spirits up, because they contains ______.

[单项选择]A small piece of fish each day may keep the heart doctor away. That’s the finding of an extensive study of Dutchmen 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 killer in the United States, with more than 550,000 deaths occurring from heart attacks each year. But researchers previously 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 follo
A. Because American people are too fat.
B. Because American people drink too much beer.
C. The author doesn’t give a definite answer.
D. Because American people don’t like sports.