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新东方英语背诵文选mp3和文本 49 Sleep
Sleet is part of a person's daily activity cycle. There are several different stages of sleep, and they too occur in cycles. If you are an average sleeper, your sleep cycle is as
新东方背诵文选2007-03-26 -
新东方英语背诵文选mp3和文本 50. Cells and Temperature
Cells cannot remain alive outside certain limits of temperature and much narrower limits mark the boundaries of effective functioning. Enzyme systems of mammals and birds are most
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新东方英语背诵文选mp3和文本 47 Folk Cultures
A folk culture is a small isolated, cohesive, conservative, nearly self-sufficient group that is homogeneous in custom and race with a strong family or clan structure and highly de
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新东方英语背诵文选mp3和文本 48 Bacteria
Bacteria are extremely small living things. While we measure our own sizes in inches or centimeters, bacterial size is measured in microns. One micron is a thousandth of a millimet
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新东方英语背诵文选mp3和文本 45.The source of Energy
A summary of the physical and chemical nature of life must begin, not on the Earth, but in the Sun; in fact, at the Sun's very center. It is here that is to be found the source of
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新东方英语背诵文选mp3和文本 46.Vision by
Human vision like that of other primates has evolved in an arboreal environment. In the dense complex world of a tropical forest, it is more important to see well that to develop a
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新东方英语背诵文选mp3和文本 43.Statistics
There were two widely divergent influences on the early development of statistical methods. Statistics had a mother who was dedicated to keeping orderly records of government units
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新东方英语背诵文选mp3和文本 44.Obtaining Fresh water from icebergs
The concept of obtaining fresh water from icebergs that are towed to populated areas and arid regions of the world was once treated as a joke more appropriate to cartoons than real
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新东方英语背诵文选mp3和文本 41.American black bears
American black bears appear in a variety of colors despite their name. In the eastern part of their range, most of these brown, red, or even yellow coats. To the north, the black b
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新东方英语背诵文选mp3和文本 42.Coal-fired power plants
The invention of the incandescent light bulb by Thomas A. Edison in 1879 created a demand for a cheap, readily available fuel with which to generate large amounts of electric power
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新东方英语背诵文选mp3和文本 39 The Salinity of Ocean Waters
If the salinity of ocean waters is analyzed, it is found to vary only slightly from place to place. Nevertheless, some of these small changes are important. There are three basic p
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新东方英语背诵文选mp3和文本 40 Cohesion-tension Theory
Atmospheric pressure can support a column of water up to 10 meters high. But plants can move water much higher; the sequoia tree can pump water to its very top more than 100 meters
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新东方英语背诵文选mp3和文本 37 Icebergs
Icebergs are among nature's most spectacular creations, and yet most people have never seen one. A vague air of mystery envelops them. They come into being ----- somewhere ------i
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新东方英语背诵文选mp3和文本 38 Topaz
Topaz is a hard, transparent mineral. It is a compound of aluminum, silica, and fluorine. Gem topaz is valuable. Jewelers call this variety of the stone "precious topaz". The best-
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新东方英语背诵文选mp3和文本 35.Oil Refining
An important new industry, oil refining, grew after the Civil war. Crude oil, or petroleum - a dark, thick ooze from the earth - had been known for hundreds of years, but little us
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新东方英语背诵文选mp3和文本 36.Plate Tectonics and Sea-floor Spreading
The theory of plate tectonics describes the motions of the lithosphere, the comparatively rigid outer layer of the Earth that includes all the crust and part of the underlying mant
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新东方英语背诵文选mp3和文本 33 Plankton浮游生物
Scattered through the seas of the world are billions of tons of small plants and animals called plankton. Most of these plants and animals are too small for the human eye to see. T
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新东方英语背诵文选mp3和文本 34 Raising Oysters
In the oysters were raised in much the same way as dirt farmers raised tomatoes- by transplanting them. First, farmers selected the oyster bed, cleared the bottom of old shells and
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新东方英语背诵文选mp3和文本 31 British Columbia
British Columbia is the third largest Canadian provinces, both in area and population. It is nearly 1.5 times as large as Texas, and extends 800 miles(1,280km) north from the Unite
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新东方英语背诵文选mp3和文本 32 Botany
Botany, the study of plants, occupies a peculiar position in the history of human knowledge. For many thousands of years it was the one field of awareness about which humans had an
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新东方英语背诵文选mp3和文本 29 Telecommuting
Telecommuting-- substituting the computer for the trip to the job ---- has been hailed as a solution to all kinds of problems related to office work.
新东方背诵文选2007-03-26
For workers it promises free -
新东方英语背诵文选mp3和文本 30 The origin of Refrigerators
By the mid-nineteenth century, the term "icebox" had entered the American language, but ice was still only beginning to affect the diet of ordinary citizens in the United States. T
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新东方英语背诵文选mp3和文本 27. Scientific Theories
In science, a theory is a reasonable explanation of observed events that are related. A theory often involves an imaginary model that helps scientists picture the way an observed e
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新东方英语背诵文选mp3和文本 28.Changing Roles of Public Education
One of the most important social developments that helped to make possible a shift in thinking about the role of public education was the effect of the baby boom of the 1950's and
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新东方英语背诵文选mp3和文本 25. Movie Music
Accustomed though we are to speaking of the films made before 1927 as "silent", the film has never been, in the full sense of the word, silent. From the very beginning, music was r
新东方背诵文选2007-03-26
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