『新东方在线托福阅读』为托福考生准备了ETS托福TPO/Official 28 Passage 1阅读练习：According to paragraph 2, what does porosity determine?真题题目及答案解析，TPO/Official 28 Passage 1阅读原文范文音频翻译

托福TPO/Official 28 Passage 1阅读原文According to paragraph 2, what does porosity determine?题目答案及解析-新东方托福官方网校手机版

世界上大多数饮用水——适合饮用的淡水——都是储存在岩石中孔隙和裂缝中的地下水。

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.

储存在地下的淡水超过地表淡水河流和湖泊总量的50倍。

There is more than 50 times as much freshwater stored underground than in all the freshwater rivers and lakes at the surface.

接近50%的地下水储存在地表下1000米以内。

Nearly 50 percent of all groundwater is stored in the upper 1,000 meters of Earth.

在地下更深层，上覆岩层的压力导致了孔隙和裂缝的闭合，从而减少了存储水的空间，并且在地下大约10km处，这些孔隙和缝隙几乎完全闭合。

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.

因此，最大的储水处在接近地表处。

The greatest water storage, therefore, lies near the surface.

Groundwater is stored in a variety of rock types.

可以抽取水的地下水蓄水处称为含水层。

A groundwater reservoir from which water can be extracted is called an aquifer.

事实上我们可以认为含水层是淡水的储蓄处。

We can effectively think of an aquifer as a deposit of water.

淡水的抽取取决于含水层的两个特性：孔隙率和渗透率。

Extraction of water depends on two properties of the aquifer: porosity and permeability.

那些由水、风或者冰晶沉积形成的沉积物（比如沙子或小岩石）之间是可以储水的。

Between sediment materials (such as sand or small rocks) that are deposited by water, wind, or glacial ice grains are spaces that can be filled with water.

孔隙的空间就被称为孔隙率，它表示孔隙空间占岩石总体积的百分比。

This pore space is known as porosity and is expressed as a percentage of the total rock volume.

孔隙率对于储水能力是很重要的，但是水要在岩石中流动，这些孔隙必须是连接的。

Porosity is important for water-storage capacity, but for water to flow through rocks, the pore spaces must be connected.

水或其他液体在相连接的空隙中流动的能力称为渗透率。

The ability of water, or other fluids, to flow through the interconnected pore spaces in rocks is termed permeability.

岩石的断裂和连接处有很高的渗透率。

Fractures and joints have very high permeability.

然而，液体在岩石的粒间空隙中需要绕着颗粒在曲折的通道里流动。弯曲的通道便阻碍了流动。

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.

流水克服阻力流动的速率和岩石的渗透率有关。

The rate at which the flowing water overcomes this resistance is related to the permeability of rock.

沉积物的分选和压实作用影响渗透率和孔隙率。

Sediment sorting and compaction influence permeability and porosity.

沉积物的分选越糟糕或者是压实越紧，它的孔隙率和渗透率就越低。

The more poorly sorted or the more tightly compacted a sediment is, the lower its porosity and permeability.

沉积岩——在地表最常见的岩石种类，也是最常见的蓄水处，因为它们用来储水的空间最多。

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.

砂岩通常可以形成较好的含水层，而细颗粒的泥岩典型地不可被渗透。

Sandstones generally make good aquifers, while finer-grained mudstones are typically impermeable.

不可被渗透的岩石被称为隔水层。

Impermeable rocks are referred to as aquicludes.

火成岩和变质岩更紧实，通常是结晶的，并且在颗粒间很少有间隙。

Igneous and metamorphic rocks are more compact, commonly crystalline, and rarely contain spaces between grains.

但是，如果在火成岩和变质岩中发生大范围的断裂并且断裂系统相互连接，即使是它们也可以作为地下水蓄水处。

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.

地下水位是地下边界，所有低于这个边界的裂痕和孔隙都存储着水。

The water table is the underground boundary below which all the cracks and pores are filled with water.

在某些情况下，地下水位到达了地表，这些地方就成为河流、湖泊和沼泽。

In some cases, the water table reaches Earth’s surface, where it is expressed as rivers, lakes, and marshes.

但是，通常地下水位在地表数十或数百米以下。

Typically, though, the water table may be tens or hundreds of meters below the surface.

地下水位不是水平的，但它往往会遵循地表轮廓，比如地球表面的形状，包括山川和峡谷这类的地貌起伏。

The water table is not flat but usually follows the contours of the topography the shape of a surface such as Earth’s, including the rise and fall of such features as mountains and valleys.

地下水位之上是包气带，雨水通过它渗透下来。

Above the water table is the vadose zone, through which rainwater percolates.

包气带的雨水下流至地下水位时，会在矿物颗粒上留下薄水层。

Water in the vadose zone drains down to the water table, leaving behind a thin coating of water on mineral grains.

包气带在接近地表处为植物的根供给水分。

The vadose zone supplies plant roots near the surface with water.

因为地下水位不是水平的而是沿着地势上下起伏的，所以地下水和地表水以相同的模式受重力影响。

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.

如果地下水位与地表交织，地下水将以喷泉的形式流出地表，或集聚于此或随后沿着排水系统流向远处。

If the water table intersects the land surface, groundwater will flow out onto the surface at springs, either to be collected there or to subsequently flow farther along a drainage.

地下水常常集聚在溪流排水处，但是在干旱地区可能会全部存留在干涸的河床表面下。

Groundwater commonly collects in stream drainages but may remain entirely beneath the surface of dry stream-beds in arid regions.

在特定的湿润年份中，因为地下水层升高并与地表交织，有些本应干旱的小段河床可能会有水流动。

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.

In paragraph 1, why does the author mention “the pressure of the overlying rock”?

According to paragraph 1, groundwater differs from the water in rivers and lakes in terms of its

The word “termed” in the passage is closest in meaning to

According to paragraph 2, what does porosity determine?

The word “compact” in the passage is closest in meaning to

According to paragraph 2, what is the relationship between permeability and porosity?

Paragraph 4 implies which of the following about the roots of plants?

Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

Look at the four squares  that indicate where the following sentence could be added to the passage. 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.  Where would the sentence best fit? Click on a square  to add the sentence to the passage.

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.

Groundwater 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 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 materials (such as sand or small rocks) that are deposited by water, wind, or glacial ice 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. Fractures and joints have very high 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. 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 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, the shape of a surface such as Earth’s, including the rise and fall of such features as mountains and valleys.  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. 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, either 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.