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老年人保证充足的维生素E供给量是为了 ( )A. 抗疲劳 B. 增进食欲C. 增强机体的抗氧化功能D. 降低胆……

老年人保证充足的维生素E供给量是为了 (    ) A.
抗疲劳  B.
增进食欲 C.
增强机体的抗氧化功能 D.
降低胆固醇

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未分类题People in the United States in the nineteenth century were haunted by the prospect that unprecedented change in the nation's economy would bring social chaos. In the years following 1820, after several decades of relative stability, the economy entered a period of sustained and extremely rapid growth that continued to the end of the nineteenth century. Accompanying that growth was a structural change that featured increasing economic diversification and a gradual shift in the nation's labor force from agriculture to manufacturing and other nonagricultural pursuits.Although the birth rate continued to decline from its high level of the eighteenth and early nineteenth century, the population roughly doubled every generation during the rest of the nineteenth century. As the population grew, its makeup also changeD.Massive waves of immigration brought new ethnic groups into the country. Geographic and social mobility-- downward as well as upward--touched almost everyonE.Local studies indicate that nearly three-quitters of the population--in the North and South, in the emerging cities of the Northeast, and in the restless rural counties of the West--changed their residence of the Northeast, and in the restless rural counties of the West--changed their residence each decadE.As a consequence, historian David Donald has written, 'Social atomization affected every segment of society,' and it seemed to many people that 'all the recognized values of orderly civilization were gradually being erodeD.'Rapid industrialization and increased geographic mobility in the nineteenth century had special implications for women because these changes tended to magnify social distinctions. As the roles men and women played in society became more rigidly defined, so did the roles they played in the homE.In the context of extreme competitiveness and dizzying social change, the household lost many of its earlier functions and the home came to serve as a haven of tranquility and order. As the size of families decreased, the roles of husband and wife became more clearly differentiated than ever beforE.In the middle class especially, men participated in the productive economy while women ruled the home and served as the custodians of civility and culturE.The intimacy of marriage that was common in earlier periods was rent, and a gulf that at times seemed unbridgeable was created between husbands and wives.What does the passage mainly discuss?A.The economic development of the United States in the eighteenth century.B.Ways in which economic development led to social changes in the United States.C.Population growth in the western United States.D.The increasing availability of industrial jobs for women in the United States.

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未分类题Deep inside a mountain near Sweatwater in East Tennessee is a body of water known as the Lost SeA.It is listed by the 'Guinness Book of World Records' as the world's largest underground lakE.The lost Sea is part of an extensive and historical cave system called Craighead Caverns.The caverns have been known and used since the days of the Cherokee Indian Nation. The cave expands into a series of huge rooms from a small opening on the side of the mountain. Approximately one mile from the entrance, in a room called 'the Council Room', many Indian artifacts have been founD.Some of the items discovered include pottery, arrowheads, weapons and jewelry.For many years there were persistent rumors of a large underground lake somewhere in a cave, but it was not discovered until 1905. In that year, a thirteen-year-old boy named Ben Sands crawled through a small opening three hundred feet undergrounD.He found himself in a large cave half filled with water.Today tourists visit the Lost Sea and ride far out onto it in glass-bottomed boats powered by electric motors. More than thirteen acres of water have been mapped out so far and still no end to the lake has been founD.Even though teams of divers have tried to explore the Lost Sea, the full extent of it is still unknown.According to the passage, the lost Sea is unique because it is ______.A.part of a historical cave systemB.the biggest underground lake in the worldC.listed in the 'Guinness Book of World Records'D.the largest body of water in Tennessee

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未分类题Volcanic fire and glacial ice are natural enemies. Eruptions at glaciated volcanoes typically destroy ice fields, as they did in 1980 when 70 percent of Mount Saint Helens ice cover was de molisheD.During long dormant intervals, glaciers gain the upper hand cutting deeply into volcanic cones and eventually reducing them to rubblE.Only rarely do these competing forces of heat and cold operate in perfect balance to create phenomenon such as the steam caves at Mount Rainier Park.Located inside Rainier's two ice-filled summit craters, these caves form. a labyrinth of tunnels and vaulted chambers about one and one-half miles in total length. Their creation depends on an unusual combination of factors that nature almost never brings together in one placE.The cave-making recipe calls for a steady emission of volcanic gas and heat, a heavy annual snowfall at an elevation high enough to keep it from melting during the summer, and a bowl-shaped crater to hold the snow.Snow accumulating yearly in Rainier's summit craters is compacted and compressed into a dense form. of ice called firn, a substance midway between ordinary ice and the denser crystalline ice that makes up glaciers. Heat rising from numerous openings (called fumaroles) along the inner crater walls melts out chambers between the rocky walls and the overlying ice pack. Circulating currents of warm air then melt additional opening in the firn ice, eventually connecting the individual chambers and, in the larger of Rainier's two craters, forming a continuous passageway that extends two-thirds of the way around the crater' s interior.To maintain the cave system, the elements of fire under ice must remain in equilibrium, Enough snow must fill the crater each year to replace that melted from below. If too much volcanic heat is discharged, the crater' s ice pack will melt away entirely and the caves will vanish along with the snows of yesteryear. If too little heat is produced, the ice replenished annually by winter snowstorms will expand, pushing against the enclosing crater wails and smothering the present caverns in solid firn icE.With what topic is the passage primarily concerned?A.The importance of snowfall for Mount Rainier.B.The steam caves of Mount Rainier.C.How ice covers are destroyeD.D.The eruption of Mount Saint Helens in 1980.

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