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托福阅读TPO28(试题+答案+译文)
归国留学证明>胖熊数据库 摘要： 托福阅读TPO28(试题+答案+译文)！阅读考试同学们不能只是做题，要注重对阅读材料的积累，平常多阅读一些文章可以培养大家的阅读能力和阅读速度。下面就一起来看看小编为同学们介绍的托福阅读TPO28(试题+答案+译文)。
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托福 阅读TPO28(试题+答案+译文)。阅读考试同学们不能只是做题，要注重对阅读材料的积累，平常多阅读一些文章可以培养大家的阅读能力和阅读速度。下面就一起来看看小编为同学们介绍的 托福阅读 TPO28(试题+答案+译文)。
托福阅读原文
【1】Most of the world’s potable water—freshwater suitable for drinking is accounted for bygroundwater, which is stored in the pores and fractures in rocks. There is more than 50 timesas much freshwater stored underground than in all the freshwater rivers and lakes at thesurface. Nearly 50 percent of all groundwater is stored in the upper 1,000 meters of Earth. Atgreater depths within Earth, the pressure of the overlying rock caus pores and cracks toclo, reducing the space that pore water can occupy, and almost complete closure occurs at adepth of about 10 kilometers. The greatest water storage, therefore, lies near the surface.
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Aquifers, Porosity and Permeabilityyoxi>sreng
【2】Groundwater is stored in a variety of rock types. A groundwater rervoir from whichwater can be extracted is called an aquifer. We can effectively think of an aquifer as a depositof water. Extraction of water depends on two properties of the aquifer: porosity andpermeability. Between diment grains are spaces that can be filled with water. This porespace is known as porosity and is expresd as a percentage of the total rock volume.Porosity is important for water—storage capacity,
but for water to flow through rocks, thepore spaces must be connected. The ability of water, or other fluids, to flow through theinterconnected pore spaces in rocks is termed permeability. In the intergranular spaces ofrocks, however, fluid must flow around and between grains in a tortuous path; this windingpath caus a resistance to flow. The rate at which the flowing water overcomes thisresistance is related to the permeability of rock.
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【3】Sediment sorting and compaction influence permeability and porosity. The more poorlysorted or the more tightly compacted a diment is, the lower its porosity and permeability.Sedimentary rocks—the most common rock type near the surface—are also the most commonrervoirs for water becau they contain the most space that can be filled with water.Sandstones generally make good aquifers, while finer-grained mudstones are typicallyimpermeable. Impermeable rocks are referred to as aquicludes. Igneous and metamorphicrocks are more compact, commonly crystalline, and rarely contain spaces between grains.However, even igneous and metamorphic rocks may act as groundwater rervoirs if extensivefracturing occurs in such rocks and if the fracture system is interconnected.
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The Water Table
