積累知識，也應該有農民積肥的勁頭，撿的範圍要寬，不要限制太多，……牛糞、人糞、羊糞都一概撿回來，讓它們統統變成有用的肥料，滋養作物的生長。以下是小編爲大家搜索整理的托福考試練習試題2017年，希望對大家有所幫助!更多精彩內容請及時關注我們應屆畢業生考試網!
Groundwater is the word used to describe water that saturates the ground, filling all theavailable spaces. By far the most abundant type of groundwater is meteoric water; this isthe groundwater that circulates as part of the water cycle. Ordinary meteoric water is waterthat has soaked into the ground from the surface, from precipitation (rain and snow) andfrom lakes and streams. There it remains, sometimes for long periods, before emerging at thesurface 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 thoseamong the particles—sand grains and tiny pebbles—of loose, unconsolidated sand and of this material, out of sight beneath the soil, are common. They are found wherever fastrivers carrying loads of coarse sediment once flowed. For example, as the great ice sheets thatcovered North America during the last ice age steadily melted away, huge volumes of waterflowed from them. The water was always laden with pebbles, gravel, and sand, known asglacial outwash, that was deposited as the flow slowed down.
The same thing happens to this day, though on a smaller scale, wherever a sediment-ladenriver or stream emerges from a mountain valley onto relatively flat land, dropping its load asthe current slows: the water usually spreads out fanwise, depositing the sediment in the formof a smooth, fan-shaped slope. Sediments are also dropped where a river slows on entering alake or the sea, the deposited sediments are on a lake floor or the seafloor at first, but will belocated inland at some future date, when the sea level falls or the land rises; such beds aresometimes thousands of meters thick.
In lowland country almost any spot on the ground may overlie what was once the bed of a riverthat has since become buried by soil; if they are now below the water’s upper surface (thewater table), the gravels and sands of the former riverbed, and its sandbars, will be saturatedwith groundwater.
So much for unconsolidated sediments. Consolidated (or cemented) sediments, too, containmillions of minute water-holding pores. This is because the gaps among the original grains areoften not totally plugged with cementing chemicals; also, parts of the original grains maybecome dissolved by percolating groundwater, either while consolidation is taking place or atany time afterwards. The result is that sandstone, for example, can be as porous as the loosesand from which it was formed.
Thus a proportion of the total volume of any sediment, loose or cemented, consists of emptyspace. Most crystalline rocks are much more solid; a common exception is basalt, a form ofsolidified 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 isnot the same as permeability, which measures the ease with which water can flow through amaterial; 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 thesample is put in a suitable dry place. But some will remain, clinging to all solid surfaces. It isheld there by the force of surface tension without which water would drain instantly from anywet surface, leaving it totally dry. The total volume of water in the saturated sample musttherefore 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 orsediment to another, even though their porosities may be the same. What happens dependson pore size. If the pores are large, the water in them will exist as drops too heavy for surfacetension to hold, and it will drain away; but if the pores are small enough, the water in them willexist as thin films, too light to overcome the force of surface tension holding them in place;then the water will be firmly held.
Paragraph 1: Groundwater is the word used to describe water that saturates the ground, fillingall 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 iswater 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 atthe surface again. At first thought it seems incredible that there can be enough space in the“solid” ground underfoot to hold all this water.
1. Which of the following can be inferred from paragraph 1 about the ground that we walk on?
○It cannot hold rainwater for long periods of time.
○It prevents most groundwater from circulating.
○It has the capacity to store large amounts of water.
○It absorbs most of the water it contains from rivers.
2. The word “incredible” in the passage is closest in meaning to
○Confusing
○Comforting
○Unbelievable
○Interesting
Paragraph 2: The necessary space is there, however, in many forms. The commonest spacesare those among the particles—sand grains and tiny pebbles—of loose, unconsolidated sandand gravel. Beds of this material, out of sight beneath the soil, are common. They are foundwherever fast rivers carrying loads of coarse sediment once flowed. For example, as the greatice sheets that covered North America during the last ice age steadily melted away, hugevolumes of water flowed from them. The water was always laden with pebbles, gravel, andsand, known as glacial outwash, that was deposited as the flow slowed down.
3. The word “out of sight” in the passage is closest in meaning to
○Far away
○Hidden
○Partly visible
○Discovered
4. According to paragraph 2, where is groundwater usually found?
○Inside pieces of sand and gravel
○On top of beds of rock
○In fast rivers that are flowing beneath the soil
○In spaces between pieces of sediment
5. The phrase “glacial outwash” in the passage refers to
○Fast rivers
○Glaciers
○The huge volumes of water created by glacial melting
○The particles carried in water from melting glaciers.
Paragraph 3: The same thing happens to this day, though on a smaller scale, wherever asediment-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 thesediment in the form of a smooth, fan-shaped slope. Sediments are also dropped where ariver slows on entering a lake or the sea, the deposited sediments are on a lake floor or theseafloor at first, but will be located inland at some future date, when the sea level falls or theland rises; such beds are sometimes thousands of meters thick.
6. All of the following are mentioned in paragraph 3 as places that sediment-laden rivers candeposit their sediments EXCEPT
○A mountain valley
○Flat land
○A lake floor
○The seafloor
Paragraph 4: In lowland country almost any spot on the ground may overlie what was once thebed of a river that has since become buried by soil; if they are now below the water’s uppersurface (the water table), the gravels and sands of the former riverbed, and its sandbars, will besaturated with groundwater.
7. The word “overlie” in the passage is closest in meaning to
○Cover
○Change
○Separate
○Surround
Paragraph 5: So much for unconsolidated sediments. Consolidated (or cemented) sediments,too, contain millions of minute water-holding pores. This is because the gaps among theoriginal grains are often not totally plugged with cementing chemicals; also, parts of theoriginal grains may become dissolved by percolating groundwater, either while consolidationis taking place or at any time afterwards. The result is that sandstone, for example, can be asporous as the loose sand from which it was formed.
8. The phrase “so much for” in the passage is closest in meaning to
○That is enough about
○Now let us turn to
○Of greater concern are
○This is related to
9. The word “plugged” in the passage is closet in meaning to
○Washed
○Dragged
○Filled up
○Soaked through
Paragraph 6: 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 isbasalt, a form of solidified volcanic lava, which is sometimes full of tiny bubbles that make itvery porous.
Paragraph 7: The proportion of empty space in a rock is known as its porosity. But note thatporosity is not the same as permeability, which measures the ease with which water can flowthrough a material; this depends on the sizes of the individual cavities and the crevices linkingthem.
10. According to paragraphs 6 and 7, why is basalt unlike most crystalline forms of rock?
○It is unusually solid
○It often has high porosity.
○It has a low proportion of empty space.
○It is highly permeable.
11. What is the main purpose of paragraph 7?
○To explain why water can flow through rock
○To emphasize the large amount of empty space in all rock
○To point out that a rock cannot be both porous and permeable
○To distinguish between two related properties of rock
Paragraph 9: The relative amount of these two kinds of water varies greatly from one kind ofrock or sediment to another, even though their porosities may be the same. What happensdepends on pore size. If the pores are large, the water in them will exist as drops too heavy forsurface tension to hold, and it will drain away; but if the pores are small enough, the water inthem will exist as thin films, too light to overcome the force of surface tension holding them inplace; then the water will be firmly held.
12. Which of the sentences below best expresses the essential information in the highlightedsentence in the passage? Incorrect choices change the meaning in important ways or leave outessential information.
○Surface tension is not strong enough to retain drops of water in rocks with large pores butit strong enough to hold on to thin films of water in rocks with small pores.
○Water in rocks is held in place by large pores and drains away from small size pores throughsurface tension.
○Small pores and large pores both interact with surface tension to determine whether a rockwill hold water as heavy drops or as a thin film.
○If the force of surface tension is too weak to hold water in place as heavy drops, the waterwill continue to be held firmly in place as a thin film when large pores exist.
Paragraph 8: Much of the water in a sample of water-saturated sediment or rock will drainfrom it if the sample is put in a suitable dry place.█ But some will remain, clinging to all solidsurfaces.█ It is held there by the force of surface tension without which water would draininstantly from any wet surface, leaving it totally dry.█ The total volume of water in thesaturated sample must therefore be thought of as consisting of water that can, and waterthat cannot, drain away.█
13. Look at the four squares [█] that indicate where the following sentence could be added tothe passage.
What, then, determines what proportion of the water stays and what proportion drainsaway?
Where would the sentence best fit? Click on a square to add the sentence to the passage.
14. Directions: An introductory sentence for a brief summary of the passage is provided lete the summary by selecting the THREE answer choices that express the mostimportant ideas in the passage. Some sentences do not belong in the summary because theyexpress ideas that are not presented in the passage or are minor ideas in the passage. Thisquestion is worth 2 points.
Much of the ground is actually saturated with water.
Answer choices
○Sediments that hold water were spread by glaciers and are still spread by rivers andstreams.
○Water is stored underground in beds of loose sand and gravel or in cemented sediment.
○The size of a saturated rock’s pores determines how much water it will retain when the rockis put in a dry place.
○Groundwater often remains underground for a long time before it emerges again.
○Like sandstone, basalt is a crystalline rock that is very porous.
○Beds of unconsolidated sediments are typically located at inland sites that were onceunderwater.
1. ○ 3
2. ○ 3
3. ○ 2
4. ○ 4
5. ○ 4
6. ○ 1
7. ○ 1
8. ○ 1
9. ○ 3
10. ○ 2
11. ○ 4
12. ○ 1
13. ○ 4
14. ○1 2 3
參考譯文：
地下水
地下水是指滲入到地下並將所有岩石空隙填滿的水。到現在爲止，雨水是最豐富的地下水資源，是地下水在水循環中的一個環節。普通的雨水會從地表、降水以及湖泊河流侵入到地下。在冒出地表之前，這些地下水有時會長時間留在地下。在我們腳下堅實的土地中竟然有足夠的空間儲存這些水，這在一開始會讓人覺得難以置信。
地下水所需的儲存空間多種多樣。鬆散的砂子和礫石間有許多顆粒和小石子，他們之間的空隙是最常見的儲存地下水的空間。由這些顆粒組成的水牀非常普遍，通常位於看不見的土壤下方，在湍急的河流曾經流過的`地方都能找到它們的蹤跡。比如，冰河時代覆蓋北美的巨大冰層逐漸融化，大量水從那兒流出。水裏總會攜帶些石子、礫石和沙石，這就是所謂的冰河期的冰水沉積，這些顆粒會隨着水流的減速而沉澱。
現代也有冰水沉積，儘管規模相對較小。凡是有攜帶泥沙的河流或者溪流從山谷流至相對平坦的地面時，砂石就隨着水流速度的減慢逐漸沉澱;水流通常呈扇形擴散，它們所攜帶的砂石也會沉澱爲光滑的扇形斜面。當河流匯入湖泊和海洋的時候也會有沉澱，這些沉澱最初在湖底或海底，但將來海平面下降或者陸地崛起時，它們就會分佈於內陸，通常厚達幾千米。
低地區域上的任何位置可能就是曾經的河牀，後續被土壤覆蓋而變成現在的樣子。如果那些河牀和沙洲現在位於地下水位之下，一定會有大量的地下水浸在它們的沙礫和沙石之間。
以上說的都是鬆散的沉積物，那些堅固的沉積物，也擁有以數萬計的毛細孔來容納水。因爲最初顆粒間的縫隙通常並未完全被粘固的化學物質塞滿，而且部分顆粒很可能在固化時或固化後被滲入的地下水溶解;結果這些砂岩最終變得和形成它的散沙一樣多孔。
因此，不管沉積物是疏鬆還是堅固，他們中一定有空間。大部分結晶體岩石都非常堅硬，但也有例外，最常見的就是玄武岩，它是一種固化的火山熔岩，經常充滿了微小氣泡，從而變得十分多孔。
岩石的多孔性就是指其中空隙的比例。但需要注意的是，多孔性與滲透性是不同的。滲透性衡量的是水滲透物質的難易程度，它取決於與單個空隙以及連接空隙間裂縫的大小。
當充滿水分的沉澱物或者岩石樣本被放置在適合的乾燥環境中時，大部分的水分會流乾，但仍有部分水會繼續附着在堅實的表面上。要不是因爲表面張力，這些水分也會立刻蒸發，僅留下完全乾燥的樣本。因此，試驗樣本的含水量既包括可以流乾的水，也包括不能流乾的水。
這兩種水的相對含量因岩石或沉積物種類不同而改變，即便它們有相同比例的空隙，還取決於空隙的大小。如果空隙很大，其中的水會形成水滴，太重足以克服吸引它的表面張力，就會流走;但如果空隙夠小，水會像薄膜一樣，太輕無法克服表面張力，從而穩穩地附着在空隙表面上。
