GMAT 考满分题库

For millennia, the Nile River flooded nearly every year as a natural consequence of heavy summer rains; in the 20th century, as the population in the region exploded, the cycle of flooding interspersed with periodic drought caused widespread suffering for the local population. In the mid-1950s, the Egyptian government concluded that a dam was necessary to enable the country's economic development to be on a par with that of Western nations. The Aswan Dam would prevent the annual flooding, generate hydroelectric power, and supply a steady source of water for residents and agricultural activities. By the 1970s, most Egyptian villages had electric power, and the dam provided approximately half of Egypt's entire output of electricity. The benefits were counteracted, however, by consequences which were sometimes slow to appear but ruinous in their long-term effects. Dams prevent silt, which renews the minerals and nutrients that make the land fertile, from flowing to downstream lands. Farmers have had to substitute artificial fertilizers, reducing profits and causing pervasive chemical pollution with deleterious effects for the nearby human, animal, and plant populations. It is difficult to draw definite conclusions about a project with such substantial and varied results, but it would be untenable to assert that the Egyptian government should never have built the Aswan Dam.