一级英语

British ColumbiaBritish Columbia is the third largest Canadian province, 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 St...

BotanyBotany, 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 th...

PlanktonScattered 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 ab...

In the past 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,...

Oil RefiningAn 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 ...

Plate Tectonics and Sea-floor SpreadingThe 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 ...

IcebergsIcebergs 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...

TopazTopaz 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 preci...

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In the traditional(传统的)marriage,　 the man worked at a job to earn money for the family ,　Most men worked in an office ,　a factory,　or some other place away from the home .Since the man e...