『新东方在线托福阅读』为托福考生准备了ETS托福TPO/Official 1 Passage 1阅读练习：What is the main purpose of paragraph 7?真题题目及答案解析，TPO/Official 1 Passage 1阅读原文范文音频翻译

托福TPO/Official 1 Passage 1阅读原文What is the main purpose of paragraph 7?题目答案及解析-新东方托福官方网校手机版

地下水指的是渗透至地下并填满所有可利用空间的水。

Groundwater is the word used to describe water that saturates the ground, filling all the available spaces.

到目前为止，作为最为丰富的地下水类型，大气水是地下水在水循环中的一环。

By far the most abundant type of groundwater is meteoric water; this is the groundwater that circulates as part of the water cycle.

常见的大气水指的是从地表、降水（雨和雪）以及湖泊和溪流渗入至地下的水。

Ordinary meteoric water is water that has soaked into the ground from the surface, from precipitation (rain and snow) and from lakes and streams.

在再次离开地表之前，地下水有时会长期存在于地下。

There it remains, sometimes for long periods, before emerging at the surface again.

在我们脚下“坚实的”土地中竟然有足够的空间能储存这么多水，乍一想会有些难以置信。

At first thought it seems incredible that there can be enough space in the “solid” ground underfoot to hold all this water.

但地下水所需的空间形式多样。

The necessary space is there, however, in many forms.

疏松的砂卵石层（沙粒和小卵石）之间的孔隙是最为常见的存储地下水的空间。

The commonest spaces are those among the particles—sand grains and tiny pebbles—of loose, unconsolidated sand and gravel.

河床就是由这些材料所构成的，虽很常见，但由于被土壤所覆盖因而不易被人发现。

Beds of this material, out of sight beneath the soil, are common.

水流湍急的河流会携带大量粗糙的泥沙，这些河流曾经流经的区域都能找到地下水的踪迹。

They are found wherever fast rivers carrying loads of coarse sediment once flowed.

例如，随着冰河时代覆盖北美的巨大冰层逐渐消融，大量水从中流出。

For example, as the great ice sheets that covered North America during the last ice age steadily melted away, huge volumes of water flowed from them.

水中总会携带一些卵石、碎石和沙砾，即所谓的冰水沉积，它们会随着水流的减缓而沉积下来。

The water was always laden with pebbles, gravel, and sand, known as glacial outwash, that was deposited as the flow slowed down.

尽管规模相对较小，如今也有同样现象发生。当携带着沉积物的河流或溪流从山谷流至平原时，砂石就会随水流速度的减缓而沉淀。由于水流经常会以扇形向四周扩展，沉积物也会形成平整的扇形斜坡。

The same thing happens to this day, though on a smaller scale, wherever a sediment-laden river or stream emerges from a mountain valley onto relatively flat land, dropping its load as the current slows: the water usually spreads out fanwise, depositing the sediment in the form of a smooth, fan-shaped slope.

当河流汇入湖泊或海洋时，沉积物最初会聚在湖底或海底。由于海平面下降或者陆地上升，它们后来会位于内陆，厚度有时达到几千米。

Sediments are also dropped where a river slows on entering a lake or the sea; the deposited sediments are on a lake floor or the seafloor at first, but will be located inland at some future date, when the sea level falls or the land rises; such beds are sometimes thousands of meters thick.

低地国家的大部分位置的下方可能都是曾经的河床，随着时间的推移被土壤所覆盖而变成现在的样子。如果那些过去的河床和沙洲的位置现在低于地下水位，那么在碎石和沙砾之间会饱含大量的地下水。

In lowland country almost any spot on the ground may overlie what was once the bed of a river that has since become buried by soil; if they are now below the water’s upper surface (the water table), the gravels and sands of the former riverbed, and its sandbars, will be saturated with groundwater.

以上内容所讲的都是松散的沉积物。

固结的（粘合的）沉积物同样拥有大量的细孔来蓄水。

Consolidated (or cemented) sediments, too, contain millions of minute water-holding pores.

这是因为原始颗粒间的缝隙通常并未完全被粘合的化学物质所填满，而且部分原始颗粒可能在固结或固结之后被所渗入的地下水所溶解。

This is because the gaps among the original grains are often not totally plugged with cementing chemicals; also, parts of the original grains may become dissolved by percolating groundwater, either while consolidation is taking place or at any time afterwards.

所以这些砂岩最终变得和构成它的散沙同样多孔。

The result is that sandstone, for example, can be as porous as the loose sand from which it was formed.

因此，无论疏松还是坚固的沉积物，其中都会有空间。

Thus a proportion of the total volume of any sediment, loose or cemented, consists of empty space.

大部分结晶岩都是实心的，但常见的玄武岩就是个例外，作为一种固化的火山熔岩，它有时会充满微小的气泡从而变得十分多孔。

Most crystalline rocks are much more solid; a common exception is basalt, a form of solidified volcanic lava, which is sometimes full of tiny bubbles that make it very porous.

岩石内部空间的比例被称为岩石的孔隙度。

The proportion of empty space in a rock is known as its porosity.

需要说明的是，孔隙度不同于渗透率。渗透率指的是用来衡量水渗透物质的难易程度，而孔隙度则取决于个体空隙以及连接孔隙间裂缝的大小。

But note that porosity is not the same as permeability, which measures the ease with which water can flow through a material; this depends on the sizes of the individual cavities and the crevices linking them.

当饱含水分的沉淀物或岩石样本被放置在适宜的干燥环境之中，大部分水分会流失。

Much of the water in a sample of water-saturated sediment or rock will drain from it if the sample is put in a suitable dry place.

但是有些水分依旧会附着于固体表面。

But some will remain, clinging to all solid surfaces.

这是由于表面张力的缘故，如果没有表面张力，这些水分会被立刻蒸发，留下完全干燥的样本。

It is held there by the force of surface tension without which water would drain instantly from any wet surface, leaving it totally dry.

因此，试验样本的总含水量既包括已流失的水，也包括存于其中的水。

The total volume of water in the saturated sample must therefore be thought of as consisting of water that can, and water that cannot, drain away.

即便孔隙度相同，这两种水的相对含量也会由于岩石或沉积物种类不同而不同。

The relative amount of these two kinds of water varies greatly from one kind of rock or sediment to another, even though their porosities may be the same.

如果孔隙太大，其中的水会聚成水滴，过重的水滴便会克服吸引它的表面张力，从而流走；但如果孔隙足够小，水由于无法克服表面张力，就会像薄膜一样牢牢吸附于孔隙表面上。

If the pores are large, the water in them will exist as drops too heavy for surface tension to hold, and it will drain away; but if the pores are small enough, the water in them will exist as thin films, too light to overcome the force of surface tension holding them in place: then the water will be firmly held.

Which of the following can be inferred from paragraph 1 about the ground that we walk on?

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

According to paragraph 2, where is groundwater usually found?

The phrase “glacial outwash” in the passage refers to

All of the following are mentioned in paragraph 3 as places that sediment-laden rivers can deposit their sediments EXCEPT

According to paragraphs 6 and 7, why is basalt unlike most crystalline forms of rock?

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. What, then, determines what proportion of the water stays and what proportion drains away?  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 Groundwater is the word used to describe water that saturates the ground, filling all the available spaces. By far the most abundant type of groundwater is meteoric water; this is the groundwater that circulates as part of the water cycle. Ordinary meteoric water is water that has soaked into the ground from the surface, from precipitation (rain and snow) and from lakes and streams. There it remains, sometimes for long periods, before emerging at the surface again. At first thought it seems incredible that there can be enough space in the “solid” ground underfoot to hold all this water. The necessary space is there, however, in many forms. The commonest spaces are those among the particles—sand grains and tiny pebbles—of loose, unconsolidated sand and gravel. Beds of this material, out of sight beneath the soil, are common. They are found wherever fast rivers carrying loads of coarse sediment once flowed. For example, as the great ice sheets that covered North America during the last ice age steadily melted away, huge volumes of water flowed from them. The water was always laden with pebbles, gravel, and sand, known as glacial outwash, that was deposited as the flow slowed down. The same thing happens to this day, though on a smaller scale, wherever a sediment-laden river or stream emerges from a mountain valley onto relatively flat land, dropping its load as the current slows: the water usually spreads out fanwise, depositing the sediment in the form of a smooth, fan-shaped slope. Sediments are also dropped where a river slows on entering a lake or the sea; the deposited sediments are on a lake floor or the seafloor at first, but will be located inland at some future date, when the sea level falls or the land rises; such beds are sometimes thousands of meters thick. In lowland country almost any spot on the ground may overlie what was once the bed of a river that has since become buried by soil; if they are now below the water’s upper surface (the water table), the gravels and sands of the former riverbed, and its sandbars, will be saturated with groundwater. So much for unconsolidated sediments. Consolidated (or cemented) sediments, too, contain millions of minute water-holding pores. This is because the gaps among the original grains are often not totally plugged with cementing chemicals; also, parts of the original grains may become dissolved by percolating groundwater, either while consolidation is taking place or at any time afterwards. The result is that sandstone, for example, can be as porous as the loose sand from which it was formed. Thus a proportion of the total volume of any sediment, loose or cemented, consists of empty space. Most crystalline rocks are much more solid; a common exception is basalt, a form of solidified volcanic lava, which is sometimes full of tiny bubbles that make it very porous. The proportion of empty space in a rock is known as its porosity. But note that porosity is not the same as permeability, which measures the ease with which water can flow through a material; this depends on the sizes of the individual cavities and the crevices linking them. Much of the water in a sample of water-saturated sediment or rock will drain from it if the sample is put in a suitable dry place.  But some will remain, clinging to all solid surfaces.  It is held there by the force of surface tension without which water would drain instantly from any wet surface, leaving it totally dry.  The total volume of water in the saturated sample must therefore be thought of as consisting of water that can, and water that cannot, drain away.  The relative amount of these two kinds of water varies greatly from one kind of rock or sediment to another, even though their porosities may be the same. What happens depends on pore size. If the pores are large, the water in them will exist as drops too heavy for surface tension to hold, and it will drain away; but if the pores are small enough, the water in them will exist as thin films, too light to overcome the force of surface tension holding them in place: then the water will be firmly held.