托福阅读TPO28(试题+答案+译文)第1篇:Groundwater
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托福阅读原文
【1】Most of the world’s potable water—freshwater suitable for drinking is accounted for by groundwater, which is stored in the pores and fractures in rocks. There is more than 50 times as much freshwater stored underground than in all the freshwater rivers and lakes at the surface. Nearly 50 percent of all groundwater is stored in the upper 1,000 meters of Earth. At greater depths within Earth, the pressure of the overlying rock causes pores and cracks to close, reducing the space that pore water can occupy, and almost complete closure occurs at a depth of about 10 kilometers. The greatest water storage, therefore, lies near the surface.
Aquifers, Porosity and Permeability
【2】Groundwater is stored in a variety of rock types. A groundwater reservoir from which water can be extracted is called an aquifer. We can effectively think of an aquifer as a deposit of water. Extraction of water depends on two properties of the aquifer: porosity and permeability. Between sediment grains are spaces that can be filled with water. This pore space is known as porosity and is expressed as a percentage of the total rock volume. Porosity is important for water—storage capacity, but for water to flow through rocks, the pore spaces must be connected. The ability of water, or other fluids, to flow through the interconnected pore spaces in rocks is termed permeability. In the intergranular spaces of rocks, however, fluid must flow around and between grains in a tortuous path; this winding path causes a resistance to flow. The rate at which the flowing water overcomes this resistance is related to the permeability of rock.
【3】Sediment sorting and compaction influence permeability and porosity. The more poorly sorted or the more tightly compacted a sediment is, the lower its porosity and permeability. Sedimentary rocks—the most common rock type near the surface—are also the most common reservoirs for water because they contain the most space that can be filled with water. Sandstones generally make good aquifers, while finer-grained mudstones are typically impermeable. Impermeable rocks are referred to as aquicludes. Igneous and metamorphic rocks are more compact, commonly crystalline, and rarely contain spaces between grains. However, even igneous and metamorphic rocks may act as groundwater reservoirs if extensive fracturing occurs in such rocks and if the fracture system is interconnected.
The Water Table
【4】The water table is the underground boundary below which all the cracks and pores are filled with water. In some cases, the water table reaches Earth’s surface, where it is expressed as rivers, lakes and marshes. Typically, though, the water table may be tens or hundreds of meters below the surface. The water table is not flat but usually follows the contours of the topography. Above the water table is the vadose zone, through which rainwater percolates. Water in the vadose zone drains down to the water table, leaving behind a thin coating of water on mineral grains. The vadose zone supplies plant roots near the surface with water.
【5】Because the surface of the water table is not flat but instead rises and falls with topography, groundwater is affected by gravity in the same fashion as surface water. Groundwater flows downhill to topographic lows. If the water table intersects the land surface, groundwater will flow out onto the surface at springs, weather to be collected there or to subsequently flow farther along a drainage. Groundwater commonly collects in stream drainages but may remain entirely beneath the surface of dry stream-beds in arid regions. In particularly wet years, short stretches of an otherwise dry stream-bed may have flowing water because the water table rises to intersect the land surface.
[Glossary]
Sediment: materials (such as sand or small rocks) that are deposited by water, wind, or glacial ice.
Topography: the shape of a surface such as Earth’s, including the rise and fall of such features as mountains and valleys.
托福阅读试题
1.In paragraph 1, why does the author mention "the pressure of the overlying rock"?
A.To show how water can be forced deep under Earth's surface.
B.To show why groundwater is more plentiful than surface freshwater.
C.To correct a commonly made error about the location of groundwater.
D.To explain why most groundwater lies near Earth's surface.
2.According to paragraph 1, groundwater differs from the water in riversand lakes in terms of its
A.portability.
B.usefulness.
C.abundance.
D.cost.
3.The word "extracted" in the passage(paragraph 2)is closest in meaning to
A.used.
B.poured.
C.removed.
D.kept out.
4.The word "termed" in the passage(paragraph 2)is closest in meaning to
A.considered.
B.called.
C.limited to.
D.caused by.
5.According to paragraph 2, what does porosity determine?
A.The rate at which the aquifer's water overcomes resistance to flow.
B.The amount of water that the aquifer can hold.
C.The likelihood that fractures and joints will occur in the aquifer.
D.The depth underground at which the aquifer lies.
6.According to paragraph 2, what is the relationship between permeability and porosity?
A.The more pores a rock has, the higher its porosity but the lower its permeability.
B.Rocks with many internal spaces that are not connected with each other will have high porosity but low permeability.
C.If water flows through a rock easily, it has high permeability but low porosity.
D.Rocks that have high permeability have high porosity and vice versa.
7.The word "compacted" in the passage(paragraphy 3)is closest in meaning to
A.hard.
B.compressed.
C.heavy.
D.deeply buried.
8.According to paragraph 3, when can igneous rock serve as an aquifer?
A.When it has many connected fractures.
B.When it lies next to metamorphic rock.
C.When it lies relatively near the surface.
D.When it is crystalline.
9.The word "coating" in the passage(paragraph 4)is closest in meaning to
A.stream.
B.barrier.
C.amount.
D.layer.
10.Paragraph 4 implies which of the following about the rootsof plants?
A.They prevent water from reaching the vadose zone.
B.They mark the boundary between the vadose zone and the water table
C.They do not typically get their water from the water table.
D.They help keep the water table from dropping farther.
11.Which of the sentences below best expresses the essential information in the highlighted sentence in the passage paragraph 5 ? Incorrect choices change the meaning in important ways or leave out essential information.
A.Groundwater only flows out of the ground if the water table intersects the land surface.
B.If the land surface and the water table intersect, groundwater can flow underground.
C.Groundwater may be drained if springs occur where the water table intersects the land surface.
D.Where the water table meets the land surface, groundwater flows out through surface springs.
12.Paragraph 5 implies which of the following about the level of the water
A.It may rise or fall from year to year, depending on annual rainfall.
B.It does not vary in arid regions.
C.It rarely intersects the land surface of most regions.
D.It is unrelated to the rate at which groundwater flows.
13. Look at the four squares [■] that indicate where the following sentence could be added to the passage.Where would the sentence best fit? This is a consequence of the slow rate of movement of the groundwater, which often prevents the water table from attaining a flat (horizontal) level.
The water table is the underground boundary below which all the cracksand pores are filled with water. In some cases, the water table reaches Earth's surface, where it is expressed as rivers, lakes and marshes. ■【A】Typically,though,the water table may be tens or hundreds of meters below the surface. ■【B】The water table is not flat but usually follows the contours of the topography. ■【C】Above the water table is the vadose zone, through which rainwater percolates. ■【D】Water in the vadosezone drains down to the water table, leaving behind a thin coating of water onmineral grains. The vadose zone supplies plant roots near the surface withwater.
14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
Most of the world's potable water is stored as groundwater in the poresand fractures of underground rock, much of it at depths of less than 1,000 meters.
A.Sedimentary rock may make poor aquifers because of tightly compacted sediment, which reduces porosity and permeability.
B.Porosity is a measure of the empty space within rock while permeability measures the degree to which water can flow freely through rock.
C.In arid regions, the water tables remain at a constant level far below the surface, preventing stream-beds from filling up even during wet years.
D.Groundwater reservoirs are characterized by the porosity and permeability of the rock in which they lie, and these factors vary according to the type of rock.
E.The vadose zone is typically dry because water does not stay in it, but instead percolates down to aquifers below or drains out through springs and streams.
F.Although the water table usually follows the contours of the land surface, its level may vary from year to year and may intersect to the surface in places.
托福阅读答案
1.在高亮部分的描写之后，本段的最后一句出现了，therefore。这里也是在说the pressure of the overlying rock导致的结果，也就是文章提到它的目的。其结果是，大部分的水储都在比较表面的地方。所以其目的就是要解释为什么水都在表面的地方。
2.对应原文第二句话，也就是将地下水和江河湖泊水进行比较的那句话。原句说more than 50 times。就证明是地下水的水量大。这里A是饮用性，原文并没有说江水不能喝。B是有用，同理。D是代价。这个就更没提到了。所以答案为C丰富。
3.extract本身是汲取，取出的意思。从原文后面一句话可以推测，因为后面说储水土层可以看作是对一笔水存款，所以前面应该是说可以取出。另外这个词的词缀ex-本身就有出的意思。那么A是使用，B是泼出，C是移动，D是隔离在外。
4.term作名词是术语，这个很常用。而这里用了其动词否定形式，那么应该是…被术语为，也就是被命名为。那么A是认为，B是叫做，C是限制于，D是由于。所以应该选B。
5.A决定于permeability of rack，对应本段最后一句。B正确，对应本段第七句(porosity is important for water-storage capacity)，这句话只要根据porosity定位就很好找。C和porosity没有直接关系。D原文就没提到。
6.对应本段第一句和第二句，即sorting和compaction会共同影响permeability，结合上一段的最后一句理解，多孔性分为两种情况，一种是孔多但是互相不联通，这时permeability不高;另一种是孔多并且互相联通，那么porosity高的同时permeability也会高。因此选择B。其他几个选项的叙述都不完整。这两者的关系并不是简单的正比例。
7.compact是压缩，紧密的意思。通过后面的and的并列内容可以推出其词义，因为and后面说rarely contain space，那就是说中间的空间很小。所以选择B压缩的。A是坚硬，C是重的，D是深埋的。
8.对应本段文章最后一句"even igneous rocks may act as groundwater…"后半句给出的就是答案，那么它说的是要有fractures并且要interconnected。所以选A。
9.Coating本来是外衣，和涂层的意思。那么A是溪流，B是障碍物，C是数量，D是层。所以D符合。
10.根据plant roots定位到本段最后一句。说vadose zone给植物根部提供了水。选项A，B，D都没提到。而只有C没有错误，因为plant roots是从vadose zone汲取的水份，而不是water table。所以选C。
11.A选项缺少了spring这个条件;B，C选项不正确。D包含了原文所有的主干部分，正确。
12.根据这段最后两句对于wet year的描写可以得出根据降雨量不同，地下水位是有变化的。所以A正确。B不正确，原文明显写到在arid regions降雨量多时干燥的溪床会有水。C也不对，整段都有大篇幅在写和land surface的intersects。D原文没提到。
13.要插入的句子说this is a consequence，那么this一定指代什么，根据后半句可以知道指代的内容应该与地下水位不是平面有关。所以C的位置符合，因为前面一句说地下水位不是平面。
14.A 错误，对应文章第三段的第三句有关于sedimentary rock的描写。根据原文，sedimentary rock是很好的aquifers，B正确，对应第二段的前四句。C正确，对应原文第二段。D错误，vadose zone中会留下thin coating所以还是会湿润。对应原文第四段。E错误，water table本非remain at a constant level，根据倒数第二句，地下水位有时会和地表交叉的。F正确，对应原文最后一段。
托福阅读译文
【1】世界上绝大部分饮用水----可以饮用的淡水----都是地下水，它们储藏在岩石孔隙和裂缝中。储藏于地下的淡水是地表淡水河流和湖泊中总水量的50倍。大约50%的地下水存在于地下深1000m以内的地层中。随深度增加，上覆岩层压力使岩石孔隙和裂缝闭合，减少了水的储存空间，而超过10公里深的地下孔隙几乎全部闭合。因此绝大部分水储存于接近地表的地层中。
水层，孔隙度和渗透率
【2】地层水储存在多种岩石中。可以取出的地下水的聚集层叫做水层。我们可以认为水层即水的聚集地层。从地层中取水取决于水层的两个因素：孔隙度和渗透率。沉积颗粒之间的空间可以储存水，这种孔隙空间由孔隙度表征。孔隙度是岩石孔隙体积与总体积的百分比。孔隙度对地层储水能力尤为重要，但欲使水从岩石中流出，孔隙之间必须相互连通。水或其它流体从相互连通的孔隙中流动的能力即为渗透率。在粒间孔发育的岩石中，流体必须在颗粒周围的曲折通道中流动;这种曲折通道会对流动产生阻力。水克服阻力流动的速率与岩石渗透率相关。
【3】沉积物的分选性和压实程度影响其渗透率和孔隙度。岩石分选越差或压实越紧则其孔隙度和渗透率越低。沉积岩----地表最常见的岩石----也是最常见的水储集层，因为它们常带有最多的可以储水的孔隙空间。砂岩一般是最好的储水层，但小颗粒的泥岩则通常不可渗透。不渗透岩层都称为隔水层。火成岩和变质岩压实更紧，通常有结晶，并几乎没有粒间孔隙。但是即便是火成岩和变质岩也可因裂缝大量发育并相互连接而成为储水层。
地下水位
【4】地下水位指地层岩石裂缝和孔隙充满水的边界。某些情况下，地下水位可能到达地表，在那里它以河流、湖泊或沼泽地的形式存在。但通常情况下地下水位位于地面数十或数百米以下。地下水位不是水平的，而是通常沿着地势起伏。地下水位以上称为包气带，在这里降水得以过滤。包气带中的水会沉降到地下水位，只在矿物颗粒表面留下一层水膜。包气带为地表附近植物根部提供水分。
【5】因为地下水位表面并非水平，而是沿着地势起伏，地下水和地表水受到重力影响的模式相同。地下水沿着下倾地层流向地势低洼处。如果地下水位与地表相交，地下水将以喷泉的形式流出地面，要么就地聚集，要么沿排水通道流向更远的地方。地下水通常在小溪中聚集，但在干旱地区也可能全部停留在干涸河床下。在特定湿润的年月里，一段干涸的河床下游可能有水流动，因为地下水位抬升到了那里的地表以上。
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