Official1托福阅读Passage3 Groundwater文本+题目原文+答案解析【雷哥托福】2018-12-28 15:19:18 发布 来源：雷哥托福 阅读量:3343
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.
Question 1 of 14：Which of the following can be inferred from paragraph 1 about the ground that we walk on?
A. It cannot hold rainwater for long periods of time.
B. It prevents most groundwater from circulating.
C. It has the capacity to store large amounts of water.
D. It absorbs most of the water it contains from rivers.
Question 2 of 14：The word “incredible ” in the passage is closest in meaning to
Question 3 of 14：The word “out of sight ” in the passage is closest in meaning to
A. far away.
C. partly visible.
Question 4 of 14：According to paragraph 2, where is groundwater usually found?
A. Inside pieces of sand and gravel.
B. On top of beds of rock.
C. In fast rivers that are flowing beneath the soil.
D. In spaces between pieces of sediment.
Question 5 of 14：The phrase “glacial outwash ” in the passage refers to
A. fast rivers.
C. the huge volumes of water created by glacial melting.
D. the particles carried in water from melting glaciers.
Question 6 of 14：All of the following are mentioned in paragraph 3 as places that sediment-laden rivers can deposit their sediments EXCEPT
A. A mountain valley.
B. Flat land.
C. A lake floor.
D. The seafloor.
Question 7 of 14：The word “overlie ” in the passage is closest in meaning to
Question 8 of 14：The phrase “So much for ” in the passage is closest in meaning to
A. that is enough about.
B. now let us turn to.
C. of greater concern are.
D. this is related to.
Question 9 of 14：The word “plugged ” in the passage is closet in meaning to
C. filled up.
D. soaked through.
Question 10 of 14：According to paragraphs 6 and 7, why is basalt unlike most crystalline forms of rock?
A. It is unusually solid.
B. It often has high porosity.
C. It has a low proportion of empty space.
D. It is highly permeable.
Question 11 of 14：What is the main purpose of paragraph 7?
A. To explain why water can flow through rock.
B. To emphasize the large amount of empty space in all rock.
C. To point out that a rock cannot be both porous and permeable.
D. To distinguish between two related properties of rock.
Question 12 of 14：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.
A. Surface tension is not strong enough to retain drops of water in rocks with large pores but it strong enough to hold on to thin films of water in rocks with small pores.
B. Water in rocks is held in place by large pores and drains away from small size pores through surface tension.
C. Small pores and large pores both interact with surface tension to determine whether a rock will hold water as heavy drops or as a thin film.
D. If the force of surface tension is too weak to hold water in place as heavy drops, the water will continue to be held firmly in place as a thin film when large pores exist.
Question 13 of 14：Look at the four squares that indicate where the following sentence could be added to the passage. Where would the sentence best fit?
What, then, determines what proportion of the water stays and what proportion drains away?
Question 14 of 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. Much of the ground is actually saturated with water.
A.Sediments that hold water were spread by glaciers and are still spread by rivers and streams..
B.Water is stored underground in beds of loose sand and gravel or in cemented sediment..
C.The size of a saturated rock’s pores determines how much water it will retain when the rock is put in a dry place..
D.Groundwater often remains underground for a long time before it emerges again..
E.Like sandstone, basalt is a crystalline rock that is very porous..
F.Beds of unconsolidated sediments are typically located at inland sites that were once underwater.
Question 1 of 14
题目解析：以下哪一项能够从第一段推出与我们走的路地有关?(Inference Question)A它不能长时间储存水。 B它阻止了大部分地下水进行水循环。 C它有能力储存大量的地下水。 D它大部分的水从河流中吸收。根据“ground that we walk on”定位到段落最后一句话“At first thought it seemsincrediblethatthere can be enough spacein the “solid” ground underfootto hold all this water.”意思是：一开始很难想象我们脚下的地有足够的空间容下这些水。 选项A错，倒数第二句“There it remains, sometimesfor long periods, before emerging at the surface again.”For long periods长时间;remain v.保持;emerge v.出现; 选项B错，段落第二句“By far themost abundanttype of groundwater is meteoric water; this is the groundwater that circulates as part of thewater cycle.”意思是：现在最丰富的地下水类型是雨水;这些雨水是进入水循环的那部分;by far最;abundant adj.富足;circulate v.循环; 选项D错，段落第三句“Ordinary meteoric water is water that has soaked into the groundfrom the surface,from precipitationandfrom lakes and streams.”意思是：平常的雨水都是那些从地表、降水和河流湖泊中渗入地下的水。soak v.渗透;precipitationn.降雨，降雪;
Question 2 of 14
题目解析："incredible: 令人难以置信的。对应C选项。A是令人困惑的;B是令人宽慰的;D是有意思的。对应原文At first thought it seems incredible that there can be enough space in the "solid" ground underfoot to hold all this water.想到credit card信用卡，credit指的是信用或者学分ible或者able表示可以……的，credible可信的，incredible难以置信的。从语境中也可以读出惊叹之意。
Question 3 of 14
题目解析："out of sight: 看不见，在视野之外。A是很遥远;B是隐藏;C是部分看的见;D是发现。根据词意，B最接近。对应原文Beds of this material, out of sight beneath the soil, are common.表面意思就是在视野之外，也就是看不见， C和D都说看见，所以错。而且far away离得很远也不代表就看不见，所以也不对。不知道的话说beneath the soil在土下面，当然也是看不见之意，所以B正确。"
Question 4 of 14
题目解析："问的是地下水在哪儿最经常在哪儿发现，找到第二句中的the commonest spaces： The commonest spaces are those among the particles—sand grains and tiny pebbles—of loose, unconsolidated sand and gravel.最常见的地方是blablabla，这个blablabla就是我们要的答案，罗列的是不同颗粒之间的空隙，所以答案D是正确的，答案把原文高度概括。"
Question 5 of 14
题目解析："glacial是冰川的，与冰川有关的，outwash是个合成词，表面意思就是冲出来的，不知道的读原文。原文说pebble, gravel and sand, known as glacial outwash，也就是说前面的三个都叫做glacial outwash，其中sand是一定知道的，不是水，所以AC错，更不是冰，B错，应该是包括沙子在内的一堆小颗粒。"
Question 6 of 14
题目解析："可在第一句找到B的flat land，B正确，A虽然有说到，但不是沉积物沉积的地点，从from可以看出，所以要选的答案是A： 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.在第二句的前半句找到C和D，CD不正确： 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..."
Question 7 of 14
题目解析："overlie: 躺在…上面;覆盖在…上面。over表在……上，lie表躺，所以overlie的意思是躺在……上，也就是A选项的cover.对应原文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原文说低地国家地上的任何一点都可能覆盖原来的河床，B改变，C分开，D围绕全都不对。"
Question 8 of 14
题目解析："so much for: 表面意思就是“已经很多了”，也就是足够的意思。A是足够;B是让我们转向;C是极受关注;D是这和…有关。根据词意，A是正确选项。对应原文So much for unconsolidated sediments. Consolidated (or cemented) sediments, too, contain millions of minute water-holding pores.代入原文，说unconsolidated未固结的沉积物已经说了很多了，下面就开始说固结的沉积物了，所以A正确，B和C都说我们马上要讨论的是未固结的沉积物，所以说反了;D表示与……相关，完全不沾边，错。"
Question 9 of 14
题目解析：与单词plugged在文中意思最接近的是(Vocabulary Question) a)Washed(冲刷) b)Dragged(拖，拉) c)Filled up(充满) d)Soaked through(渗入) 解析：plug v.堵，赛，插上;含义与充满是一样的。
Question 10 of 14
题目解析："以crystalline rock和basalt为关键词定位至第六段的最后一句：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.原文说大部分crystalline rock是固化比较好的，但basalt是个例外，说basalt更加porous，孔隙率更高，所以B正确。"
Question 11 of 14
Question 12 of 14
题目解析："原文的结构是如果孔隙大，就不容易hold，如果孔隙小，就容易hold。A完全正确。选项B说反，应该是孔隙大的话水会流走;C的interact to determine改变原句的意思和逻辑，错;D选项在若干处都偷换了原文的概念，完全不对。"
Question 13 of 14
题目解析："待插入句说多少流走多少剩下是什么决定的，所以之前必须得说一部分流走了一部分剩下了，原文最后一句才说到这个，所以D是答案。貌似B选项之前也说了流走和剩下，但B之后有个it is held there，这个it指的是前文的留下来的水，所以与上文过渡紧密，不能插入句子。"
Question 14 of 14
题目解析：Much of the ground is actually saturated with water. 很大部分地是充满水的。 A储存水的沉淀物曾今被冰川扩散并且现在还被河流溪水扩散。 B储存在地下的水都处在沙子和沙砾基底或者在坚固的沉淀物中。 C当被放置在干燥的地方时，饱和岩石空隙的大小决定了有多少水会被保留。 D重新出现之前，地下水会在地下保持很久。 E与砂岩一样，玄武岩是一种特别多孔的晶体岩石。 F松散沉积物的基地通常位于那些曾今在水下的内陆地点。选项A对，第二段“For example, asthe great ice sheetsthat covered …..”提到被冰川扩散;第三段“The same thing happens to this day, …..wherever asediment-laden river or streamemerges from a mountain valley onto relatively flat land,….” 选项B对，第二段讲到必要的空间在沙子和沙砾的微粒间的空隙中;第五段第二句“Consolidated(cemented) sediments, too , contain millions of minute water-holding pores.” 选项C对，最后一段讲到“What happensdepends on pore size.”最后一段也是为了解决倒数第二段提出的问题：什么决定哪部分水留下来，哪部分水流干? 选项D错，这是第一段的一个细节。 选项E错，原文没讲到basalt和sandstone一样。选项F错，原文没有提到松散沉积物的基地typically都在曾今是水下的陆地。因此，答案是：A、B、C.