2003-8-27

The wide variety of climates in North America has helped spawn a complex pattern of soil regions. In general, the realm’s soils also reflect the broad environmental partitioning into “humid America” and “arid America.” Where annual precipitation exceeds 20 inches (50 centimeters),soils in humid areas tend to be acidic in chemical content, Since crops  

(5 ) do best in soils that are neither acidic(higher in acid content) nor alkaline(higher in salt content).fertilization is necessary to achieve the desired level of neutrality between the     two. Arid America’s soils are typically alkaline and must be fertilized back toward     neutrality by adding acidic compounds. Although many of these dryland soils, particularly     in the Great Plains, are quite fertile, European settlers learned over a century ago that

(10) water is the main missing ingredient in achieving their agricultural potential. In the  1970’s, certain irrigation methods were perfected and finally provided a real opportunity     to expand more intensive farming west from the Central Lowland into the drier portions     of the Great Plains. Glaciation also enhanced the rich legacy of fertile soils in the central     United States,both from the deposition of mineral-rich glacial debris left by meltwater

(15) and from thick layers of fine wind-blown glacial material, called loess, in and around the     middle laceName>MississippilaceName> laceType>ValleylaceType>.

       Natural vegetation patterns could be displayed on a map of North America, but the     enormous human modification of the North American environment in modern times has     all but reduced this regionalization scheme to the level of the hypothetical. Nonetheless,

(20) the humid America-arid America dichotomy is still a valid generalization: the natural  vegetation of areas receiving more than 20 inches of water yearly is forest, whereas the     drier climates give rise to a grassland cover. The forests of North America tent to make a broad transition by latitude. In the Canadian North, needle-leaf forests dominate, but

these coniferous trees become mixed with broadleaf deciduous trees as one crosses the

(25) border into the Northeast United States. As one proceeds toward the Southeast, broadleaf vegetation becomes dominant. Arid America mostly consists of short-grass prairies or stepper. The only areas of true desert are in the Southwest.

Natural vegetation patterns could be displayed on a map of North America, but the     enormous human modification of the North American environment in modern times has     all but reduced this regionalization scheme to the level of the hypothetical. Nonetheless,

(20) the humid America-arid America dichotomy is still a valid generalization:

如果从语法上面来说, 我认为这个this regionalization 应该从前才对呀.

好难，我也只能做完题反推才能～～

还是因为still所以上下有联系了？（这样说会不会被大家打的呀？）

要是不看文章直接定位做，的确有难度，看起来还是要理解意思来做的。

又仔细看了一遍, 还是觉得C对. 看整个这一段:

Natural vegetation patterns could be displayed on a map of North America, but the     enormous human modification of the North American environment in modern times has     all but reduced this regionalization scheme to the level of the hypothetical. Nonetheless, the humid America-arid America dichotomy is still a valid generalization: the natural  vegetation of areas receiving more than 20 inches of water yearly is forest, whereas the     drier climates give rise to a grassland cover. The forests of North America tent to make a broad transition by latitude. In the Canadian North, needle-leaf forests dominate, but these coniferous trees become mixed with broadleaf deciduous trees as one crosses the border into the Northeast United States. As one proceeds toward the Southeast, broadleaf vegetation becomes dominant. Arid America mostly consists of short-grass prairies or stepper. The only areas of true desert are in the Southwest.

先说自然植被分布的格局本来是可以在地图上显示出来的. 但是, 因为人们的改造使这种分布格局变得hypothetical 了.  然后又转折, 但是, 基本的干湿两分还是可以的.  然后举例, 全部都是说植物的地理分布问题.

natural vegetation pattern应该比较确切一点, 而distinction between humid and acrid 太广了一点吧. 比如说它可以包括上面说得土壤酸碱度等等.

请大家继续讨论.

错了，对不起