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文章一
American Black Bears
美國黑熊
American black bears appear in a variety of colors despite their name. In the eastern part of their range, most of these bears have shiny black fur, but in the west they grow brown, red, or even yellow coats. To the north, the black bear is actually gray or white in color. Even in the same litter, both brown and black furred bears may be k bears are the smallest of all American bears, ranging in length from five to six feet, weighing from three hundred to five hundred pounds. Their eyes and ears are small and their eyesight and hearing are not as good as their sense of smell.
Like all bears, the black bear is timid, clumsy, and rarely dangerous, but if attacked, most can climb trees and cover ground at great speeds. When angry or frightened, it is a formidable k bears feed on leaves, herbs, roots, fruit, berries, insects, fish, and even larger animals. One of the most interesting characteristics of bears, including the black bear, is their winter sleep. Unlike squirrels, woodchucks, and many other woodland animals, bears do not actually hibernate. Although the bear does not eat during the winter months,sustaining itself from body fat, its temperature remains almost normal, and it breathes regularly four or five times per minute.
Most black bears live alone, except during mating season. They prefer to live in caves, hollow logs, or dense thickets. A litter of one to four cubs is born in January or February after a gestation period of six to nine months, and they remain with their mother until they are fully grown or about one and a half years old. Black bears can live as long as thirty years in the wild, and even longer in game preserves set aside for them.
美國黑熊雖然被叫區域的東部，大部分黑 熊長有富有光澤的黑毛，但在西部，他們則長着棕色、紅色甚至是黃色的毛。
在北部，黑熊其實長着灰色或白色的毛。 就是在一胎所生的小熊中，都可能混雜棕毛和黑毛。 黑熊是 所有美洲熊中最小的，5～6 英尺長，300～500磅重。它們的眼睛和耳朵都很小，他們的視 力和聽覺不如嗅覺那樣好。 像所有的熊一樣，黑熊膽小，笨拙，很少具有危險性。 但如果受到攻擊，大部分黑熊會以很快的速度爬上樹和奔跑。 當發怒或受驚嚇時，黑熊會成爲可 怕的對手。
黑熊以樹葉、草、樹根、水果、漿果、昆蟲、魚，甚至更大的動物爲食。 熊類， 包括黑熊的最有趣的一個特點是他們的冬眠。與松鼠、旱獺和其它別的林地動物不同，熊 並不真正地冬眠。 雖然熊在冬天的幾個月中不吃東西，靠體內脂肪維持生命，但它們的體溫保持正常，並有規律地一分鐘呼吸 4 或 5 次。除交配季節外，大多數黑熊獨自生活。 他 們喜歡住在洞裏、空心的大木頭裏或茂密的樹叢裏。 經過 6到 9 個月的懷孕期後一胎 1～4 個小熊在 1 月或 2 月出生。 它們同母熊住在一起，直到它們完全長大，即 1 歲半左右。黑熊在野外可以活到長達 30 年，在專門的保護區中甚至能活得更長。
文章二
Coal-fired Power Plants
火力發電廠
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 the bill, and it fueled the earliest power stations (which were set up at the end of the nineteenth century by Edison himself). As more power plants were constructed throughout the country, the reliance on coal increased. Since the First World War, coal fired power plants have accounted for about half of the electricity produced in the United States each year. In 1986 such plants had a combined generating capacity of 289, 000 megawatts and consumed 83percent of the nearly 900 million tons of coal mined in the country that year. Given the uncertainty in the future growth of nuclear power and in the supply of oil and natural gas, coalfired power plants could well provide up to 70 percent of the electric power in the United States by the end of the century.
Yet, in spite of the fact that coal has long been a source of electricity and may remain one for many years (coal represents about 80 percent of United States fossil-fuel reserves), it has actually never been the most desirable fossil fuel for power plants. Coal contains less energy per unit of weight than natural gas or oil; it is difficult to transport, and it is associated with a host of environmental issues, among them acid rain. Since the late 1960’s problems of emission control and waste disposal have sharply reduced the appeal of coal-fired power plants. The cost of ameliorating these environmental problems along with the rising cost of building a facility as large and complex as a coal-fired power plant, have also made such plants less attractive from a purely economic perspective.
Changes in the technological base of coal-fired power plants could restore their attractiveness, however. Whereas some of these changes are evolutionary and are intended mainly to increase the productivity of existing plants, completely new technologies for burning coal cleanly are also being developed.