新东方背诵文选 L31 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 United States border. It
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
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 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 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 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 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 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 "precious topaz". The best-known precious topaz
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 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 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 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 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 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 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
