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  3. A Delicate Balance In 1965 the American statesman Adlai E Stevenson said, "We all travel together, passengers on a little sp

A Delicate Balance In 1965 the American statesman Adlai E Stevenson said, "We all travel together, passengers on a little sp

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问题                    A Delicate Balance
    In 1965 the American statesman Adlai E Stevenson said, "We all travel together, passengers on a little spaceship, dependent on its vulnerable supplies of air and soil. We manage to survive by the care, work, and love we give our fragile craft." Our planet is indeed fragile. Every living thing on this planet is part of a complicated web of life, for no organism lives entirely on its own. Every organism is affected by all that surrounds it whether living or nonliving. And in turn each organism has some effect on its surroundings.
    Even the most elementary understanding of ecology requires knowledge of this cause/effect relationship all organisms have on each other. Every thing we do to our environment will in one way or another affect the quality of life we experience on this tiny spaceship. If we want the quality of life to be high, we must be more aware that nature is a finely balanced mechanism and that it will not tolerate the abuse we have been giving it. Consider the following examples of human ignorance concerning the delicate balance of nature.
    Aswan and Other Fables
    "Once there was a country that desperately needed food and energy for its growing population. It happened that one of the most magnificent rivers in the world flowed through this country. Each year the river deposited tons of mineral-rich silt on its fertile flood plain before it reached the sea. "Why not dam the river," said the country’s leaders, "and use the water to irrigate more land, control the annual spring flooding of the river, and provide hydroelectric power all at the same time?" The result of this modern-day fairy tale is known as the billion- dollar Aswan High Dam of Egypt, and not all Egyptians are living happily ever after.
    "For one thing, as water backed up behind the dam, almost 100,000 Egyptians had to choose between giving up their family homes and being submerged along with ancient and priceless temples that were part of Egypt’s cultural heritage. But there have been far more devastating results. Now that the Nile River floodplain is deprived of its annual enrichment with silt, artificial fertilizer has to be trucked in at a cost of 100 million dollars a year — a cost carried by the subsistence farmers who make, on the average, less than a hundred dollars a year each. Furthermore, now there is nothing to wash away the previous year’s silt buildup in the soil. And with silt deposits no longer compensating for erosion, the fertile river delta is shrinking — and an alarming part of what remains has completely dried up. Restoring the delta with pumps, drains, and wells may cost more than the dam itself."
    "Ironically, evaporation as well as bottom seepage from the new lake filling in behind the dam is so great that the lake basin may never fill up to predicted levels. So nobody can live around the lake because nobody knows for sure where the shoreline will be. More seriously, there is less water to go around than there was before. And even though some 700,000 new acres (about 1.6 million hectares) have been opened up for agriculture, the population outgrew the potential food increase even before the dam was finished. At the same time, with the nutrient-rich flow of the Nile turned off, another major food source-the sardines, shrimp, and mackerel that flourished in the enriched waters off the delta — has declined catastrophically. Worse yet, the lake and the irrigation networks have so accelerated the spread of blood flukes that half the Egyptian populace are now carriers of schistosomiasis (血吸虫病). In irrigated areas, where eight out of ten humans live, women can expect to live only to age twenty-seven, men to age twenty-five."
The Hawaiian Goose
    Another clear example of human ignorance of nature’s delicate balance is seen in the near extinction of the Hawaiian Goose or Nene. It was estimated in the late eighteenth century that the population of Hawaii’s unique variety of goose stood at about 25,000. In a matter of fifty years the population had dropped to approximately thirty birds. There were undoubtedly multiple causes for the decline in the Nene population, and virtually all of them resulted, either directly or indirectly, from humans.
    The most disastrous activities of humans included hunting with firearms, ranching activities, and the building of beach resorts. There is little doubt that the Nene’s near extinction was hastened after shotguns were brought to Hawaii. It seems reasonable to assume that many more Nenes were killed when guns became common. In a similar fashion, as people moved further inland on the islands they began to open more and more land for the development of ranches and beach resorts. These developments forced the geese out of their natural nesting and breeding ranges. As these ranches and resorts became more plentiful, the Nene population accordingly decreased.
    The most harmful indirect effect of humans’ activities was the introduction of animals such as cattle, goats, mongooses, and game birds. When cattle were first brought to the islands, King Kamehameha proclaimed a ten-year protection of the animals. They were allowed to roam the islands unrestrained. They multiplied rapidly, and as they did they moved further and further into the virgin forests, destroying many of the plants that provided food and shelter for the Nene. The goats that were introduced to the islands were even more destructive to the Nene’ natural habitat. Because the goats were more agile, not only could they reach the plants at the lower elevations, but they also moved into the high-lands. In 1882, the mongoose was introduced to Hawaii in hopes that it would control the rats that were doing great damage in the sugar cane fields. The mongoose neither solved the rat problem nor remained in the sugar cane fields. As it moved out of the cane fields, it did what it does naturally: it became a predator of ground-nesting birds-including the Nene. The game birds introduced to Hawaii (quail, turkey, and guinea hen) all encroached on the Nene’s already severely limited natural range. With the limited land space that an island has, the Nene had no escape route and no time to build defenses against these rapidly arriving unnatural opponents.
    By the 1940s, the Nene population had dwindled to a number so low that almost nothing could be done to save this unique, tame, land-living goose. It had become a classic example of our unconscious destruction of nature.
    Mosquito Plague
    Still another famous incident drives home the intricate relationships within our ecosystem. Some years ago, large quantities of DDT were used by the World Health Organization in a program of mosquito control in Borneo. Soon the local people, spared a mosquito plague, began to suffer a plague of caterpillars, which devoured the thatched roofs of their houses, causing them to fall in. The habits of the caterpillars limited their exposure to DDT, but predatory wasps that had formerly controlled the caterpillars were devastated.
    Further spraying was done indoors to get rid of houseflies. The local gecko lizards, which previously had controlled the flies, continued to gobble their corpses — now full of DDT. As a result, the geckos were poisoned, and the dying geckos were caught and eaten by house cats. The cats received doses of DDT, which had been concentrated as it passed from fly to gecko to cat, and the cats died. This led to another plague, now of rats. They not only devoured the people’s food but also threatened them with yet another plague — this time the genuine article, bubonic plague. The government of Borneo became so concerned that cats were parachuted into the area in an attempt to restore the balance.
    These are only three of many examples of our misunderstanding and mistreatment of the environment. Every thing we do to the environment will in one way or another affect other living things around us. Every time a factory dumps chemicals, a power plant burns coal, a corporation builds a new resort, or hunters overkill a species of animal, a chain reaction is started that may have harmful, long-range consequences. The more we try to understand, control, and compensate for those consequences before they are set in motion, the more harmoniously we will be able to live on this delicately balanced "tiny spaceship".
In a matter of fifty years the population of the Nene ______.
选项 A、increased from thirty to 2500
B、increased from thirty to 25,000
C、dropped from 2500 to thirty
D、dropped from 25,000 to thirty
答案D
解析 原文意思为：据估计夏威夷雁的数量在50年内由25,000降到了30。很明显D项“dropped from 25,000 to thirty”与之相符，故选之。
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