托福阅读背景知识：农作物灌溉
在2014年6月28日的托福阅读考试中有这样一道题：农作物灌溉。查字典出国留学网()小编提醒大家：问题及解决类的文章。解决方法还分为有效和无效两种。不能带着主观意识去妄自预测文章内容走势。一定要做到忠于并彻底读懂原文。
托福阅读真题再现：
第一段：一群人迁移到某个地区。因为这个地方雨水少，所以就有那种方式来种植。第二段是第一种办法，建大坝，但是下大雨的话容易冲垮。
第三段：找个好点的地方永久居住。
第四段：打一枪换一个地方。但是要保证人口少好让地共来得及恢复。
第五段：地区全部种植之后互相分配收成好的地区给不好的地共分食物，但是这是个很复杂的政治什么的统治结构。
第六段：唯一一个能保留千年的办法就是自给自足。
解析：问题及解决类的文章。解决方法还分为有效和无效两种。不能带着主观意识去妄自预测文章内容走势。一定要做到忠于并彻底读懂原文。
相关背景：
Irrigation is the artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall. Additionally, irrigation also has a few other uses in crop production, which include protecting plants against frost, suppressing weed growth in grain fields and preventing soil consolidation. In contrast, agriculture that relies only on direct rainfall is referred to as rain-fed or dryland farming.
Irrigation systems are also used for dust suppression, disposal of sewage, and in mining. Irrigation is often studied together with drainage, which is the natural or artificial removal of surface and sub-surface water from a given area.
Irrigation has been a central feature of agriculture for over 5000 years, and was the basis of the economy and society of numerous societies, ranging from Asia to Arizona.
North America
Main article: Hohokam
In North America, the Hohokam were the only culture to rely on irrigation canals to water their crops, and their irrigation systems supported the largest population in the Southwest by AD 1300. The Hohokam constructed an assortment of simple canals combined with weirs in their various agricultural pursuits. Between the 7th and 14th centuries, they also built and maintained extensive irrigation networks along the lower Salt and middle Gila rivers that rivaled the complexity of those used in the ancient Near East, Egypt, and China. These were constructed using relatively simple excavation tools, without the benefit of advanced engineering technologies, and achieved drops of a few feet per mile, balancing erosion and siltation. The Hohokam cultivated varieties of cotton, tobacco, maize, beans and squash, as well as harvested an assortment of wild plants. Late in the Hohokam Chronological Sequence, they also used extensive dry-farming systems, primarily to grow agave for food and fiber. Their reliance on agricultural strategies based on canal irrigation, vital in their less than hospitable desert environment and arid climate, provided the basis for the aggregation of rural populations into stable urban centers.
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