新东方背诵文选 L49 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 follows. When you fis

新东方背诵文选 L47 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 developed rituals. Ord

新东方背诵文选 L48 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 millimeter: a pinhead is abo

新东方背诵文选 L36.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 mantle. The lithosphere(

新东方背诵文选 L50. 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 efficient only withi

新东方背诵文选 L44.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 life. But now it is

新东方背诵文选 L41.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 bear is actually gray

新东方背诵文选 L43.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 (states and statist

新东方背诵文选 L42.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. Coal seemed to fit

新东方背诵文选 L46.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 an acute sense of sme

新东方背诵文选 L45.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 the energy that the

新东方背诵文选 L37 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 ------in faraway, frigid wat

新东方背诵文选 L34 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 other debris, then

新东方背诵文选 L40 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 above the ground. U

新东方背诵文选 L33 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. They drift about lazi

新东方背诵文选 L38 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

新东方背诵文选 L35.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 use had ever been made

新东方背诵文选 L39 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 processes that cause

新东方背诵文选 L32 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 anything more than the

34．A Man's A Man For A' That

34．A Man's A Man For A' ThatIs there for honest povertyThat hings his head, an' a' that ?(2)The coward slave, we pass him byWe dare be poor for a' that! For a' that, an' a' that,Our toils obscure, an' a' that;The rank is but the guinea's stamp(3),T