Living organisms play anessentialrole in soilformation. Thenumerousplants and animals living in the soilreleaseminerals from the parentmaterialfrom which soil is formed,supplyorganicmatter, aid in the translocation (movement) and aeration of the soil, and help protect the soil fromerosion. The types of organisms growing or living in the soil greatly influence the soil'sphysicaland chemical characteristics. In fact, formaturesoils in many parts of the world, thepredominanttype of naturalvegetationis considered the most important direct influence on soil characteristics. For thisreason, a soil scientist can tell a greatdealabout theattributesof the soil in anygivenareasimplyfrom knowing what kind offlorathe soil supports. Thus prairies andtundraregions, which havecharacteristicvegetations, also havecharacteristicsoils.

Thequantityand total weight of soilfloragenerallyexceedthat of soilfauna. By far the mostnumerousand smallest of the plants living in soil arebacteria. Underfavorableconditions, a million or more of these tiny, single-celled plants caninhabiteach cubic centimeter of soil. It is thebacteria, more than any other organisms, that enable rock or other parentmaterialtoundergothegradualtransformationto soil. Somebacteriaproduceorganicacids that directly attack parentmaterial, breaking it down and releasing plant nutrients. Othersdecomposeorganiclitter(debris) to formhumus(nutrient-richorganicmatter). A third group ofbacteriainhabits therootsystems of plants called legumes. These include many important agricultural crops, such asalfalfa, clover, soybeans, peas, and peanuts. Thebacteriathat legumeshostwithintheirrootnodules (small swellings on theroot) changenitrogengas from theatmosphereintonitrogencompounds that plants are able to metabolize, aprocess, known asnitrogenfixation, that makes the soil morefertile. Othermicroscopicplants also are important in soildevelopment. For example, in highlyacidicsoils where fewbacteriacansurvive,fungifrequently become thechiefdecomposers oforganicmatter.

Morecomplexforms ofvegetationplay severalvitalroles withrespectto the soil. Trees, grass, and other large plantssupplythebulkof the soil'shumus. The minerals released as these plantsdecomposeon the surfaceconstitutean importantnutrientsourcefor succeeding generations of plants as well as for other soil organisms. Inaddition, trees canextendtheir roots deepwithinthe soil and bring up nutrients from far below the surface. These nutrientseventuallyenrichthe surface soil when the tree drops its leaves or when it dies and decomposes. Finally, treesperformthevitalfunctionof slowing waterrunoffand holding the soil in place with theirrootsystems, thus combatingerosion. The increasederosionthat often accompanies agricultural use of sloping land isprincipallycaused by theremovalof its protective cover of naturalvegetation.

Animals also influence soilcomposition. The faunal counterparts ofbacteriaare protozoa. These single-celled organisms are the mostnumerousrepresentatives of the animalkingdom, and, likebacteria, a million or more can sometimesinhabiteach cubic centimeter of soil. Protozoa feed onorganicmatter andhastenitsdecomposition. Among other soil-dwelling animals, the earthworm is probably the most important. Under exceptionallyfavorableconditions, up to a million earthworms (with a total body weight exceeding 450 kilograms) mayinhabitanacreof soil. Earthwormsingestlarge quantities of soil, chemicallyalterit, and excrete it asorganicmatter called casts. The casts form a high-quality naturalfertilizer. Inaddition, earthworms mix of soil bothverticallyand horizontally, improving aeration anddrainage.

Insects such as ants and termites also can beexceedinglynumerousunderfavorableclimaticand soil conditions. Inaddition, mammals such as moles,fieldmice, gophers, andprairiedogs sometimes are present insufficientnumbers to havesignificantimpacton the soil. These animalsprimarilywork the soil mechanically. As a result, the soil is aerated broken up,fertilized, and brought to the surface, hastening soildevelopment.

Questions:
question_stem: The word "attributes" in the passage is closest in meaning to
choices: tag: A
text: properties

tag: B
text: surrounding

tag: C
text: sources

tag: D
text: nutrients
answer_key: A
explanation: 本题考查的词汇定位到原文这一句：For this reason, a soil scientist can tell a great deal about the attributes of the soil in any given area simply form knowing what kind of flora the soil supports. 因为这个原因，一个研究土壤的科学家可以说出关于任意地区的土壤成分的很多知识，单纯凭借它上面的植被种类。此处 attribute 意思是组成成分，内容物，选项 A 意为性质，财产；选项 B 意为环境，周边；选项 C 意为资源；选项 D 意为营养物质。选项 A 最符合。

question_stem: According to paragraph 1, which of the following factors is the most important in determining the characteristics of a mature soil?
choices: tag: A
text: The kinds of minerals in the parent material.

tag: B
text: The extent of erosion in the surrounding area.

tag: C
text: The amount of air that circulates through the soil.

tag: D
text: The kind of vegetation associated with the soil.
answer_key: D
explanation: 本题的关键词在于：most important 和 in determining the characteristics of a mature soil，根据这个短语定位回原文这一句：In fact, for mature soils in many parts of the world, the predominant type of natural vegetation is considered the most important direct influence on soil characteristics. 本句大意为：实际上，对于很多地方的成熟土壤，自然植被里的优势物种被认为会给土壤特征施加最重要的直接影响。选项 D 说与土壤有关的植物，正确；选项 A 的矿物质，选项 B 的周围土地的侵蚀和选项 C 的空气数量都与原文无关。

question_stem: 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 of leave out essential information.
choices: tag: A
text: Legumes make the soil more fertile by hosting bacteria in their root nodules.

tag: B
text: Nitrogen fixation makes compounds that plants and bacteria in legumes can metabolize.

tag: C
text: Bacteria living in the roots of legumes makes the soil more fertile by producing nitrogen compounds that plants can metabolize.

tag: D
text: The root nodules of legumes contain bacteria, nitrogen gas from the atmosphere, and nitrogen compounds that plants can metabolize.
answer_key: C
explanation: 定位到本题文中高亮的句子：The bacteria that legumes host within their root nodules (small swellings on the root) change nitrogen gas from the atmosphere into nitrogen compounds that plants are able to metabolize, a process, known as nitrogen fixation,  that makes the soil more fertile. 这一句讲的是与豆类植物共生的一种细菌的固氮作用，这种细菌可以把空气里的氮气变成含氮化合物，让植物可以进行新陈代谢。选项 C 是同义转述，正确。选项 A 说豆类通过在根的肿块里养细菌让土壤更有营养，错误；选项 B 说固氮作用产生的营养物质植物和细菌都可以用，不对，是只有植物也就是豆类可以用；选项 D 是说豆类的根的肿块里有细菌，空气和含氮化合物，原文里并没有说有空气，错误。选择 C。

question_stem: According to paragraph 2, which of the following statements about soil creation is true?
choices: tag: A
text: Soil creation requires that there be more plants than animals in any given location.

tag: B
text: Soil is created from the organic debris left over when bacteria decompose.

tag: C
text: Soil creation occurs when a cubic centimeter of existing soil contains abundant organic material.

tag: D
text: Soil is created as a results of bacteria breaking down rocks and organic material.
answer_key: D
explanation: 本题需要看第二段大部分内容。选项 A 没有提到，属于无中生有；选项 B 原文里提到了，但是原文中说的是细菌去 decompose 别的东西，不是 decompose 细菌自己，错误；选项 C 说土壤在有了足够的有机物以后就可以产生，不对，应该还需要细菌；选项 D 正确，依据是原文这句话：It is the bacteria, more than any other organisms,  that enable rock or other parent material to undergo the gradual transformation to soil.

question_stem: In paragraph 2, why does the author mention the activity of fungi in acidic soils?
choices: tag: A
text: To demonstrate that fungi are capable of nitrogen fixation under certain conditions.

tag: B
text: To supports the claim that microscopic plants besides bacteria contribute to soil development.

tag: C
text: To show that fungi play a different role from bacteria in decomposing organic matter.

tag: D
text: To account for the survival rate of microscopic plants in highly acidic soils.
answer_key: B
explanation: 本句根据 the activity of fungi in acidic soils 定位回原文：Other microscopic plants also are important in soil development. For example, in highly acidic soils where few bacteria can survive, fungi frequently become the chief decomposers of organic matter. 由 for example 可以看出来，fungi 的出现是为了作为例子证明前面那句话，即其他的微生物也对于土壤的发展有重要的作用。选项 B 符合。选项 A 和 D 说的东西定位处没有提，选项 C 说真菌在降解有机物的时候发挥了跟细菌不同的作用，原文里也没提。

question_stem: The word "bulk" in the passage is closet in meaning to
choices: tag: A
text: composition

tag: B
text: largest part

tag: C
text: richest part

tag: D
text: quality
answer_key: B
explanation: 根据 bulk 定位回原文这一句：Trees, grass, and other large plants supply the bulk of the soil's humus. 枝条，小草和其他大的植物提供了土壤里大部分的腐殖质。bulk 意思是大块的，大部分的，选项 B 最大的部分最符合。选项 A 是成分，选项 C 是最富的部分，选项 D 是质量。都不能选。

question_stem: According to paragraph 3, how do trees benefit other plants?
choices: tag: A
text: Trees make deep-lying nutrients available to plants whose roots do not extend very far into the soil.

tag: B
text: When trees decompose, they release nutrients minerals deep into the soil.

tag: C
text: Humus from trees provides nutrients for plants with roots that extend deep within the soil.

tag: D
text: When trees die and decompose, they make available a large space for generations of other plants to grow.
answer_key: A
explanation: 本题关键词是 trees 和 benefit other plants，根据这两个词定位回原文，发现从 More complex forms of vegetation play several vital roles with respect to the soil.开始都是 benefit，第一点是分解出来的矿物质提供营养，第二点是树根可以把地下深处的营养带到地表，第三点是减缓水流流速，防止水土流失。原文里分别有 in addition 和 finally 做指示词，很清楚。本题 A 选项符合第二点，正确。选项 B 与第二点反了，不是把营养送入地下；选项 C 在这里没有提及；选项 D 说树木死掉以后可以给后来的树木腾出大量空间，也没有提到。

question_stem: Paragraph 3 supports which of the following inferences about the effect of vegetation on soil?
choices: tag: A
text: The root systems of most crops are unable to prevent erosion on sloping ground.

tag: B
text: Without a cover of vegetation, fast running water is likely to disappear from the ground surface before it can erode much of the soil.

tag: C
text: The roots of trees and other large plants remove much water from the ground, making the soil dry and likely to be eroded by the wind.

tag: D
text: Areas that naturally have little vegetation, such as deserts, are more easily eroded than is agricultural land that has been cleared of its natural vegetation.
answer_key: A
explanation: 本题根据 the effect of vegetation on soil 定位回这一句：The increased erosion that often accompanies agricultural use of sloping land is principally caused by the removal of its protective cover of natural vegetation. 移除了植被保护层的种农作物的斜坡很容易被侵蚀。这说明只有植物可以帮助防止斜坡坍塌。选项 A 说大多数庄稼的根不能阻止水土流失，是符合原文的。选项 B 说没有树的根，水流会消失，不对；选项 C 说树根会移走地表水，让土壤变干，原文里没有说；选项 D 说没有植被的土地与移除了植被的耕地相比更容易被侵蚀，这个原文里没提，无从比较。

question_stem: The word "hasten" in the passage is closet
choices: tag: A
text: aid

tag: B
text: begin

tag: C
text: accelerate

tag: D
text: ensure
answer_key: C
explanation: 本题根据考察词汇定位回这一句：Protozoa feed on organic matter and hasten its decomposition. 这一句的意思是：Protozoa 吃的是有机物，并加速它们的降解。hasten 在这里是加快加速的意思，选项 A 是帮助，选项 B 是开始，选项 C 是加速，选项 D 是确保，选项 C 最符合题意。

question_stem: According to paragraph 4, earthworms do all the following to help soils develop EXCEPT
choices: tag: A
text: eat waste matter

tag: B
text: mix the soil in different directions

tag: C
text: change the chemistry of the soil

tag: D
text: create a natural fertilizer
answer_key: A
explanation: 本题关键词是 earthworms 和 help soils develop，根据它们定位回这两句：Earthworms ingest large quantities of soil, chemically alter it, and excrete it as organic matter called casts. The casts form a high-quality natural fertilizer. In addition, earthworms mix of soil both vertically and horizontally, improving aeration and drainage. 选项 B 对应 mix of soil both vertically and horizontally，选项 C 对应 chemically alter it，选项 D 对应 casts form a high-quality natural fertilizer，只有选项 A 没有提到，选择 A。

question_stem: The word "exceedingly" in the passage is closest in meaning to
choices: tag: A
text: surprisingly

tag: B
text: relatively

tag: C
text: reliably

tag: D
text: extremely
answer_key: D
explanation: 本题根据考察的词汇定位回原文这一句：Insects such as ants and termites also can be exceedingly numerous under favorable climatic and soil conditions. 这一句大意为：昆虫在适宜的气候和土壤条件下也可以繁殖得很多很多。exceedingly 意为很，是表示强调程度的。选项 A 是惊奇的，选项 B 是相对的，选项 C 是可信的可靠的，选项 D 是尤其的，极其的，表强调，合适。选择 D。

question_stem: According to paragraph 5, in which of the following ways do some mammals help soils develop?
choices: tag: A
text: They prevent insects from feeding on nutrients that enrich the soil.

tag: B
text: They break up the soil as they move through it.

tag: C
text: They remove waste matter that would otherwise contaminate the soil.

tag: D
text: They ensure that fertilizer remains in the soil.
answer_key: B
explanation: 本题关键词是 mammal 和 soils develop。根据关键词定位回原文最后一段：These animals primarily work the soil mechanically. As a result, the soil is aerated broken up, fertilized, and brought to the surface, hastening soil development. 这些哺乳动物可以打碎土壤，给土壤施肥，把这些土壤带到地表，加速土壤的化学变化。选项 B 符合这三点里的第一点。其余三个选项都没有提到。选择 B。