上點課臺,下載上點課臺,下載TOEFL希刪！閱讀原文：Thedeserts,whichalreadyoccupyapproximatelyafourthoftheEarth'slandsurface,haveinrecentdecadesbeenincreasingatanalarmingpace.Theexpansionofdesertlikeconditionsintoareaswheretheydidnotpreviouslyexistiscalleddesertification.Ithasbeenestimatedthatanadditionalone-fourthoftheEarth'slandsurfaceisthreatenedbythisprocess.沙漠已經占據了地球陸地面積約四分之一，而且最近幾十年正以驚人的速度擴張。沙漠化是指類似沙漠的環境漫延到原本并非沙漠的區域。據估計，地球表面另外四分之一的地方正面臨沙漠化威脅。Desertificationisaccomplishedprimarilythroughthelossofstabilizingnaturalvegetationandthesubsequentacceleratederosionofthesoilbywindandwater.Insomecasestheloosesoilisblowncompletelyaway,leavingastonysurface.Inothercases,thefinerparticlesmayberemoved,whilethesand-sizedparticlesareaccumulatedtoformmobilehillsorridgesofsand.沙漠化主要通過以下過程實現：首先自然植被不斷減少，隨后風力和雨水加速了土壤的腐蝕。有的時候松散的土壤全部被風刮走，留下石質化的表層；其它情況下細小的沙粒可能會被吹走，而正常沙粒大小的砂子不斷堆積，從而形成移動的沙丘或者沙脊。Evenintheareasthatretainasoilcover,thereductionofvegetationtypicallyresultsinthelossofthesoil'sabilitytoabsorbsubstantialquantitiesofwater.Theimpactofraindropsontheloosesoiltendstotransferfineclayparticlesintothetiniestsoilspaces,sealingthemandproducingasurfacethatallowsverylittlewaterpenetration.Waterabsorptionisgreatlyreduced;consequentlyrunoffisincreased,resultinginacceleratederosionrates.Thegradualdryingofthesoilcausedbyitsdiminishedabilitytoabsorbwaterresultsinthefurtherlossofvegetation,sothatacycleofprogressivesurfacedeteriorationisestablished.即便是在保留了土壤表層的區域，植被減少也已成為土壤大量吸取地下水的能力下降的典型因素。雨水對松散土壤的沖擊會把細小的粘土顆粒沖到土壤空隙中，封閉了土壤并降低土地表層水的滲透率。地表對水的吸收急劇減少，大量水資源流失，因此土壤的腐蝕率也隨即增加。地表吸收水分的能力進一步弱化使得土壤越發干燥，導致植被的進一步流失，于是便形成了土壤沙漠化的惡性循環。Insomeregions,theincreaseindesertareasisoccurringlargelyastheresultofatrendtowarddrierclimaticconditions.Continuedgradualglobalwarminghasproducedanincreaseinaridityforsomeareasoverthepastfewthousandyears.Theprocessmaybeacceleratedinsubsequentdecadesifglobalwarmingresultingfromairpollutionseriouslyincreases.在一些地方，沙漠面積的擴大很大程度上歸因于干燥的氣候條件。在過去的幾千年里，不斷增加的溫室效應使得一些地方干旱問題愈發嚴重。倘若空氣污染帶來的溫室效應繼續惡化，沙漠化進程會在未來數十年內加速實現。Thereislittledoubt,however,thatdesertificationinmostareasresultsprimarilyfromhumanactivitiesratherthannaturalprocesses.Thesemiaridlandsborderingthedesertsexistinadelicateecologicalbalanceandarelimitedintheirpotentialtoadjusttoincreasedenvironmentalpressures.Expandingpopulationsaresubjectingthelandtoincreasingpressurestoprovidethemwithfoodandfuel.Inwetperiods,thelandmaybeabletorespondtothesestresses.Duringthedryperiodsthatarecommonphenomenaalongthedesertmargins,though,thepressureonthelandisoftenfarinexcessofitsdiminishedcapacity,anddesertificationresults.然而，可以肯定的是，大部分地區沙漠化主要都是由于人類活動造成，而非自然條件導致。沙漠邊緣的半干旱土地所處的生態平衡環境非常脆弱，環境壓力持續增加，而這些半干旱區域適應環境壓力的能力極其有限。人口數量的增加使得人們不斷向土地施壓，依其提供食物和燃料。在濕潤的季節里，土地興許能夠應付這些壓力。但是在干旱的季節里，在沙漠周邊的土地上，存在著這樣一個十分普遍的現象：人類對土地施加的壓力遠遠超過了土地自身減壓的能力，因此最終形成了沙漠。Fourspecificactivitieshavebeenidentifiedasmajorcontributorstothedesertificationprocesses:overcultivation,overgrazing,firewoodgathering,andoverirrigation.Thecultivationofcropshasexpandedintoprogressivelydrierregionsaspopulationdensitieshavegrown.Theseregionsareespeciallylikelytohaveperiodsofseveredryness,sothatcropfailuresarecommon.Sincteheraisingofmostcropsnecessitatesthepriorremovalofthenaturalvegetation,cropfailuresleaveextensivetractsoflanddevoidofaplantcoverandsusceptibletowindandwatererosion.導致沙漠化的主要因素有四個：過度種植，過度放牧，過分砍伐，過度灌溉。由于人口密度增加，人們對糧食作物的種植已經擴展到日益干燥的區域進行。這些區域很有可能經常會發生干旱，所以農作物種植失敗是很正常的事情。大多數農作物的種植需要事先移除天然植被，而農作物欠收后又會留下大面積荒地，非常容易被風力和雨水侵蝕。Theraisingoflivestockisamajoreconomicactivityinsemiaridlands,wheregrassesaregenerallythedominanttypeofnaturalvegetation.Theconsequencesofanexcessivenumberoflivestockgrazinginanareaarethereductionofthevegetationcoverandthetramplingandpulverizationofthesoil.Thisisusuallyfollowedbythedryingofthesoilandacceleratederosion.在半干旱地區，草坪是主要的天然植被，家畜飼養是當地的一項主要經濟活動。在一個地區過量飼養家畜會導致植被覆蓋面積減少，土地被大量踐踏和碾碎。通常，隨之而來的就是土地硬化和加速侵蝕。Firewoodisthechieffuelusedforcookingandheatinginmanycountries.Theincreasedpressuresofexpandingpopulationshaveledtotheremovalofwoodyplantssothatmanycitiesandtownsaresurroundedbylargeareascompletelylackingintreesandshrubs.Theincreasinguseofdriedanimalwasteasasubstitutefuelhasalsohurtthesoilbecausethisvaluablesoilconditionerandsourceofplantnutrientsisnolongerbeingreturnedtotheland.在很多國家木材是用來做飯和加熱的最主要燃料。人口增加帶來的壓力促使人們大量砍伐木材，導致許多城市和鄉村周圍大面積樹木和灌木減少。同時人們大量使用烘干的動物排泄物作為替代燃料同樣對土壤不利，因為這些珍貴的土壤成分調節劑和植物營養資源將不會再回歸至土壤當中。Thefinalmajorhumancauseofdesertificationissoilsalinizationresultingfromoverirrigation.Excesswaterfromirrigationsinksdownintothewatertable.Ifnodrainagesystemexists,thewatertablerises,bringingdissolvedsaltstothesurface.Thewaterevaporatesandthesaltsareleftbehind,creatingawhitecrustallayerthatpreventsairandwaterfromreachingtheunderlyingsoil.造成土地沙漠化的最后一個主要人為因素在于人類過度灌溉導致土壤的鹽堿化。灌溉多余的水滲透到地下水位。假如沒有排水系統的存在，那么地下水位上升，把溶解的鹽分帶到土壤表面。水分蒸發后，鹽分留在了表面，形成白色的地殼層，這一地殼層阻止了空氣和水接觸地底下的土壤。Theextremeseriousnessofdesertificationresultsfromthevastareasoflandandthetremendousnumbersofpeopleaffected,aswellasfromthegreatdifficultyofreversingorevenslowingtheprocess.Oncethesoilhasbeenremovedbyerosion,onlythepassageofcenturiesormillenniawillenablenewsoiltoform.Inareaswhereconsiderablesoilstillremains,though,arigorouslyenforcedprogramoflandprotectionandcover-cropplantingmaymakeitpossibletoreversethepresentdeteriorationofthesurface.沙漠化問題異常嚴重，這是因為有佷廣闊的地區和數量龐大的人群都受到了沙漠化的影響，而且要想逆轉沙漠化的進程甚至減緩沙漠化的速度都面臨著巨大的困難。一旦土壤被侵蝕，需要再經過幾百到上千年的時間才會產生新的土壤。那些大量土壤仍保存完好的地方，亟需一個嚴謹而有力的保護政策和植被覆蓋計劃來保護現有土地。第1題：ThewordthreatenedinthepassageisclosestinmeaningtoA：RestrictedB：EndangeredC：PreventedD：Rejected解析：threatened受到威脅的，很容易選出B選項，endangered,使危險。依據上下文，前句說什么是desertification,本句說還有1/4的土地被這種過程（沙漠化）如何，也很容易猜出選項。第2題：Accordingtoparagraph3,thelossofnaturalvegetationhaswhichofthefollowingconsequencesforsoil?A：IncreasedstonycontentB：ReducedwaterabsorptionC：IncreasednumbersofspacesinthesoilD：Reducedwaterrunoff解析：ThisisaFactualInformationquestionaskingforspecificinformationthatcanbefoundinparagraph3.Thecorrectanswerischoice2,reducedwaterabsorption.Theparagraphexplicitlystatesthatthereductionofvegetationgreatlyreduceswaterabsorption.Choice4,reducedwaterrunoff,explicitlycontradictstheparagraph,soitisincorrect.The"spacesinthesoil"arementionedinanothercontext:theparagraphdoesnotsaythattheyincrease,sochoice3isincorrect.Theparagraphdoesnotmentionchoice第3題：TheworddelicateinthepassageisclosestinmeaningtoA：FragileB：PredictableC：ComplexD：Valuable解析：ThisisaVocabularyquestion.Thewordbeingtestedisdelicate.Itishighlightedinthepassage.Thecorrectanswerischoice1,"fragile,"meaning"easilybroken."Delicatehasthesame?〃q?-1〃meaningas"fragile."第4題：Accordingtoparagraph5,indryperiods,borderareashavedifficultyA：AdjustingtostressescreatedbysettlementB：RetainingtheirfertilityafterdesertificationC：ProvidingwaterforirrigatingcropsD：Attractingpopulationsinsearchoffoodandfuel解析：根據dryperiod定位本段末句，說在沙漠邊緣典型的干旱期，對土地的壓力經常遠遠超過土讀弱化的能力，從而導致沙漠化。并且前句說，在濕潤季節，土地或許能回應這些壓力。前后對比可知干旱期不能回應這些壓力。A正確，本句和前句內容概括。B錯，沙漠化之后的結果沒有提到。C錯，沒有提到。D錯，沒有提到。第5題：ThewordprogressivelyinthepassageisclosestinmeaningtoA：OpenlyB：ImpressivelyC：ObjectivelyD：Increasingly解析：progressively,由詞跟gress走和前綴pro向前可知詞義大致是進步的，前進的，增加的。D正確。A公開的，B印象深刻的，C客觀的都不對。第6題：Accordingtoparagraph6,whichofthefollowingisoftenassociatedwithraisingcrops?A：LackofproperirrigationtechniquesB：FailuretoplantcropssuitedtotheparticularareaC：RemovaloftheoriginalvegetationD：Excessiveuseofdriedanimalwaste解析：ThisisaFactualInformationquestionaskingforspecificinformationthatcanbefoundinparagraph6.Thecorrectanswerischoice3,"removaloftheoriginalvegetation."Sentence4ofthisparagraphsaysthat"theraisingofmostcropsnecessitatesthepriorremovalofthenaturalvegetation,上點課臺,下載上點課臺,下載TOEFL希刪！anexplicitstatementofanswerchoice3.Choice1,lackofproperirrigationtechniques,isincorrectbecausetheparagraphmentions"overirrigation"asacauseofdesertification.Noirrigation"techniques"arediscussed.Choices2and4,failuretoplantsuitablecropsanduseofanimalwaste,arenotdiscussed.第7題：ThephrasedevoidofinthepassageisclosestinmeaningtoA：ConsistingofB：HiddenbyC：ExceptforD：Lackingin解析：devoidof缺乏，很容易選出D。根據上下文，本句后段說，andsusceptibletowindandwatererosion.該段讀懂也能猜出詞義。A組成，B隱藏，C除外都不對。第8題：Accordingtoparagraph9,thegroun'dsabsorptionofexcesswaterisafactorindesertificationbecauseitcanA：InterferewiththeirrigationoflandB：LimittheevaporationofwaterC：RequiremoreabsorptionofairbythesoilD：Bringsaltstothesurface解析：根據absorptionofexcesswater定位，找到excesswaterfromirrigationsinksintothewatertable.后句提到，bringingdissolvedsaltstothesurface.可知D正確。A錯，沒有提到。B錯，沒有提到。C錯，沒有提到。第9題：AllofthefollowingarementionedinthepassageascontributingtodesertificationEXCEPTA：SoilerosionB：GlobalwarmingC：InsufficientirrigationD：Theraisingoflivestock解析：ThisisaNegativeFactualInformationquestionaskingforspecificinformationthatcanbefoundinthepassage.Choice3,"insufficientirrigation,"isthecorrectanswer.Choice1,"soilerosion,"isexplicitlymentionedinparagraph2asoneoftheprimarycausesofdesertification,soitisnotthecorrectanswer.Choice2,"globalwarning,"ismentionedasacauseofdesertificationinparagraph4,soitisincorrect.Choice4,"raisingoflivestock,"isdescribedinparagraph7asanothercauseofdesertification,soitisincorrect.Thepassageincludesexcessiveirrigationasacauseofdesertification,butnotitsopposite,insufficientirrigation,sothatisthecorrectanswer.第10題：Whichofthesentencesbelowbestexpressestheessentialinformationinthehighlightedsentenceinthepassage?Incorrectchoiceschangethemeaninginimportantwaysorleaveoutessentialinformation.A：Desertificationisasignificantproblembecauseitissohardtoreverseandaffectslargeareasoflandandgreatnumbersofpeople.B：Slowingdowntheprocessofdesertificationisdifficultbecauseofpopulationgrowththathasspreadoverlargeareasofland.C：Thespreadofdesertsisconsideredaveryseriousproblemthatcanbesolvedonlyiflargenumbersofpeopleinvariouscountriesareinvolvedintheeffort.D：Desertificationisextremelyhardtoreverseunlessthepopulationisreducedinthevastareasaffected.解析：原句含有一個弱因果關系resultsfrom.沙漠化的嚴重性來自3個方面：受影響土地面積大，受影響人口多，恢復困難。A正確，只改變了原句敘述順序。B錯，改變了因果關系。C錯，增加了條件關系。D錯，增加了條件關系。第11題：Itcanbeinferredfromthepassagethattheauthormostlikelybelieveswhichofthefollowingaboutthefutureofdesertification?A：Governmentswillactquicklytocontrolfurtherdesertification.B：Thefactorsinfluencingdesertificationoccurincyclesandwillchangeinthefuture.C：Desertificationwillcontinuetoincrease.D：Desertificationwillsoonoccurinallareasoftheworld解析：推理題，由整篇文章，尤其是末段可以推斷出作者對于沙漠化持悲觀態度，C與此態度一致。A不能推出，末段末句說，嚴格的政策可能may改變沙漠化進程，但沒有A確定推斷。B錯，3段提到有可能惡性循環，但不能確定改變。D錯，該選項過于悲觀。文章首段提到additionalone-fourthoftheEarth'slandsurface,但沒有說全部地區第12題：Lookatthefoursquares[]thatindicatewherethefollowingsentencecanbeaddedtothepassage.Wherewouldthesentencebestfit?Thiseconomicrelianceonlivestockincertainregionsmakeslargetractsoflandsusceptibletoovergrazing.解析：插入句說，特定地區對于牲畜的經濟依賴導致大片土地易于被過度放牧。由B位置后句consequence推斷，正好和插入句構成因果關系。