練習閱讀分冊答案

TPO1- TPO1-Theoriginof TPO1-TimberlineVegetationon TPO2-Desert TPO2-Early TPO2-TheOriginsof TPO3 TPO3Long-TermStabilityof TPO3DepletionoftheOgallala TPO30Roleofyin TPO30ThePaceofEvolutionary Tpo30TheInventionoftheMechanical TPO-31SpeciationinGeographicallyIsolated TPO-31EarlyChildhood TPO-31Savanna TPO1-Groundwateristhewordusedtodescribewaterthatsaturatestheground,fillingalltheavailablespaces.Byfarthemostabundanttypeofgroundwaterismeteoricwater;thisisthegroundwaterthatcirculatesaspartofthewatercycle.Ordinarymeteoricwateriswaterthathassoakedintothegroundfromthesurface,fromprecipitation(rainandsnow)andfromlakesandstreams.Thereitremains,sometimesforlongperiods,beforeemergingatthesurfaceagain.Atfirstthoughtitseemsincrediblethattherecanbeenoughspaceinthe“solid”groundunderfoottoholdallthiswater.Thenecessaryspaceisthere,however,inmanyforms.Thecommonestspacesarethoseamongtheparticles—sandgrainsandtinypebbles—ofloose,unconsolidatedsandandgravel.Bedsofthismaterial,outofsightbeneaththesoil,arecommon.Theyarefoundwhereverfastriverscarryingloadsofcoarsesedimentonceflowed.Forexample,asthegreaticesheetsthatcoveredNorthAmericaduringthelasticeagesteadilymeltedaway,hugevolumesofwaterflowedfromthem.Thewaterwasalwaysladenwithpebbles,gravel,andsand,knownasglacialoutwash,thatwasdepositedastheflowsloweddown.Thesamethinghappenstothisday,thoughonasmallerscale,whereverasediment-ladenriverorstreamemergesfromamountainvalleyontorelativelyflatland,dropitsloadasthecurrentslows:thewaterusuallyspreadsoutfanwise,depositingthesedimentintheformofasmooth,fan-shapedslope.Sedimentsarealsodroppedwhereariverslowsonenteringalakeorthesea,thedepositedsedimentsareonalakefloorortheseaflooratfirst,butwillbelocatedinlandatsomefuturedate,whenthesealevelfallsorthelandrises;suchbedsaresometimesthousandsofmetersInlowlandcountryalmostanyspotonthegroundmayoverliewhatwasoncethebedofariverthathassince eburiedbysoil;iftheyarenowbelowthewater’suppersurface(thewatertable),thegravelsandsandsoftheformerriverbed,anditssandbars,willbesaturatedwithSomuchforunconsolidatedsediments.Consolidated(orcemented)sediments,too,containmillionsofminutewater-holdingpores.Thisisbecausethegapsamongtheoriginalgrainsareoftennottotallypluggedwithcementingchemicals;also,partsoftheoriginalgrainsmay dissolvedbypercolatinggroundwater,eitherwhileconsolidationistakingceoratanytimeafterwards.Theresultisthatsandstone,forexample;canbeasporousastheloosesandfromwhichitwasformed.Thusaproportionofthetotalvolumeofanysediment,looseorcemented,consistsofemptyspace.Mostcrystallinerocksaremuchmoresolid;acommonexceptionisbasalt,aformofsolidifiedvolcaniclava,whichissometimesfulloftinybubblesthatmakeitveryporous.Theproportionofemptyspaceinarockisknownasitsporosity.Butnotethatporosityisnotthesameaspermeability,whichmeasurestheeasewithwhichwatercanflowthroughamaterial;thisdependsonthesizesoftheindividualcavitiesandthecreviceslinkingthem.Muchofthewaterinasampleofwater-saturatedsedimentorrockwilldrainfromitifthesampleisputinasuitabledryce.Butsomewillremain,clingingtoallsolidsurfaces.Itisheldtherebytheofsurfacetensionwithoutwhichwaterwoulddraininstantlyfromanywetsurface,leavingittotallydry.Thetotalvolumeofwaterinthesaturatedsamplemustthereforebethoughtofasconsistingofwaterthatcan,andwaterthatcannot,drainaway.Therelativeamountofthesetwokindsofwatervariesgreatlyfromonekindofrockorsedimenttoanother,eventhoughtheirporositiesmaybethesame.Whathappensdependsonporesize.Iftheporesarelarge,thewaterinthemwillexistasdropstooheavyforsurfacetensiontohold,anditwilldrainaway;butiftheporesaresmallenough,thewaterinthemwillexistasthinfi ,toolightto etheofsurfacetensionholdingthemince;thenthewaterwillbefirmlyheld.n.waterbeladenby到目前為spreadadv呈扇形somuchiceprep在adv.相對adv.穩(wěn)定lakewatern.clingadv.立即e【Passage1Groundwateristhewordusedtodescribewaterthatsaturatestheground,fillingalltheavailablespaces.Byfarthemostabundanttypeofgroundwaterismeteoricwater;thisisthegroundwaterthatcirculatesaspartofthewatercycle.①Ordinarymeteoricwateriswaterthathassoakedintothegroundfromthesurface,fromprecipitation(rainandsnow)andfromlakesandstreams.Thereitremains,sometimesforlongperiods,beforeemergingatthesurfaceagain.②Atfirstthoughtitseemsincrediblethattherecanbeenoughspaceinthe“solid”groundunderfoottoholdallthiswater.用橫 From是whichis，其先行詞是water自降水（雨和雪用橫 it屬于形式主語，thatWhatcanyouinferfromthephrase“Atfirst土地中竟然有足夠的空間 這么些水【Passage2Thenecessaryspaceisthere,however,inmanyforms.③Thecommonestspacesarethoseamongtheparticles—sandgrainsandtinypebbles—ofloose,unconsolidatedsandandgravel.Bedsofthismaterial,outofsightbeneaththesoil,arecommon.Theyarefoundwhereverfastriverscarryingloadsofcoarsesedimentonceflowed.Forexample,asthegreaticesheetsthatcoveredNorthAmericaduringthelasticeagesteadilymeltedaway,hugevolumesofwaterflowedfromthem.④Thewaterwasalwaysladenwithpebbles,gravel,andsand,knownasglacialoutwash,thatwasdepositedastheflowsloweddown.用橫 破折號之間的成分叫做同位語，用來解釋andsand用橫 thatpebbles，gravelandsand，它們整體被稱作glacialoutwash水流 而沉淀，這就叫做冰水沉積【Passage3⑤Thesamethinghappenstothisday,thoughonasmallerscale,whereverasediment-ladenriverorstreamemergesfromavalleyontorelativelyflatland,dropitsloadasthecurrentslows:thewaterusuallyspreadsoutfanwise,depositingthesedimentintheformofasmooth,fan-shapedslope.⑥Sedimentsarealsodroppedwhereariverslowsonenteringalakeorthesea,thedepositedsedimentsareonalakefloorortheseaflooratfirst,butwillbelocatedinlandatsomefuturedate,whenthesealevelfallsorthelandrises;suchbedsaresometimesthousandsofmeters用橫 Wherever用橫 句中的謂語共有四處，aredroppedareonwillbelocated,arethick.【Passage4⑦Inlowlandcountryalmostanyspotonthegroundmayoverliewhatwasoncethebedofariverthathassince eburiedbysoil;iftheyarenowbelowthewater’suppersurface(thewatertable),thegravelsandsandsoftheformerriverbed,anditssandbars,willbesaturatedwith用橫 whatthat3.翻譯：低地國家的任何位置都可能就是曾經的河床，后續(xù)被下水位之下，一定會有大量的水浸在它們的沙子和礫石之間【Passage5Somuchforunconsolidatedsediments.Consolidated(orcemented)sediments,too,containmillionsofminutewater-holdingpores.Thisisbecausethegapsamongtheoriginalgrainsareoftennottotallypluggedwithcementingchemicals;also,partsoftheoriginalgrainsmay dissolvedbypercolatinggroundwater,eitherwhileconsolidationistakingceoratanytimeafterwards.Theresultisthatsandstone,forexample,canbeasporousastheloosesandfromwhichitwasformed.【Passage6Thusaproportionofthetotalvolumeofanysediment,looseorcemented,consistsofemptyspace.⑧Mostcrystallinerocksaremuchmoresolid;acommonexceptionisbasalt,aformofsolidifiedvolcaniclava,whichissometimesfulloftinybubblesthatmakeitveryporous.1.用橫 which見的例外這是一種的火山巖有時會充滿泡泡使其變得非常多【Passage7Theproportionofemptyspaceinarockisknownasitsporosity.Butnotethatporosityisnotthesameaspermeability,whichmeasurestheeasewithwhichwatercanflowthroughamaterial;thisdependsonthesizesoftheindividualcavitiesandthecreviceslinkingthem.【Passage8Muchofthewaterinasampleofwater-saturatedsedimentorrockwilldrainfromitifthesampleisputinasuitabledryce.Butsomewillremain,clingingtoallsolidsurfaces.Itisheldtherebytheofsurfacetensionwithoutwhichwaterwoulddraininstantlyfromanywetsurface,leavingittotallydry.Thetotalvolumeofwaterinthesaturatedsamplemustthereforebethoughtofasconsistingofwaterthatcan,andwaterthatcannot,drain【Passage9Therelativeamountofthesetwokindsofwatervariesgreatlyfromonekindofrockorsedimenttoanother,eventhoughtheirporositiesmaybethesame.Whathappensdependsonporesize.Iftheporesarelarge,thewaterinthemwillexistasdropstooheavyforsurfacetensiontohold,anditwilldrainaway;butiftheporesaresmallenough,thewaterinthemwillexistasthinfi,toolightto etheofsurfacetensionholdingthemince;thenthewaterwillbefirmlyheld.TPO1-TheoriginofInseekingtodescribetheoriginsoftheater,onemustrelyprimarilyonspeculation,sincethereislittleconcreteevidenceonwhichtodraw.Themostwidelyacceptedtheory,championedbyanthropologistsinthelatenineteenthandearlytwentiethcenturies,envisionstheaterasemergingoutofmythandritual.Theprocessperceivedbytheseanthropologistsmaybesummarizedbriefly.Duringtheearlystagesofitsdevelopment,asociety esawareofsthatappeartoinfluenceorcontrolitsfoodsupplyandwell-being.Havinglittleunderstandingofnaturalcauses,itattributesbothdesirableandundesirableoccurrencestosupernaturalormagicals,anditsearchesformeanstowinthefavoroftheses.Perceivinganapparentconnectionbetweencertainactionsperformedbythegroupandtheresultitdesires,thegrouprepeats,refinesandformalizesthoseactionsintofixedceremonies,orrituals. Stories(myths)maythengrowuparoundaritual.Frequentlythemythsincluderepresentativesofthosesupernaturalsthattheritescelebrateorhopetoinfluence.Performersmaywearcostumesandmaskstorepresentthemythicalcharactersorsupernaturalsintheritualsorin panyingcelebrations.Asapeople esmoresophisticated,itsconceptionsofsupernaturalsandcausalrelationshipsmaychange.Asaresult,itmayabandonormodifysomerites.Butthemythsthathavegrownuparoundtheritesmaycontinueaspartofthegroup’soraltraditionandmayevencometobeactedoutunderconditionsdivorcedfromtheserites.Whenthisoccurs,thefirststephasbeentakentowardtheaterasanautonomousactivity,andthereafterentertainment andaestheticvaluesmaygraduallysociallyefficaciousconcerns.

theformermysticalAlthoughorigininritualhaslongbeenthemostpopular,itisbynomeanstheonlytheoryabouthowthetheatercameintobeing.Storylinghasbeenproposedasonealternative.Underthistheory,relatingandlisteningtostoriesareseenasfundamentalhumanpleasures.Thus,therecallingofanevent(ahunt,battle,orotherfeat)iselaboratedthenarrator’spantomimeandim ationandeventuallythrougheachrolebeingassumedbyadifferent Acloselyrelatedtheoryseestheaterasevolvingoutofdancesthatareprimarilypantomimic,rhythmicalorgymnastic,orfromimitationsofanimalnoisesandsounds.Admirationfortheperformer’sskill,virtuosity,andgraceareseenasmotivationforelaboratingtheactivitiesintofullyrealizedtheatricalperformances.Inadditiontoexploringthepossibleantecedentsoftheater,scholarshavealsotheorizedaboutthemotivesthatledpeopletodeveloptheater.Whydidtheaterdevelop,andwhywasitvaluedafteritceasedtofulfillthefunctionofritual?Mostanswersfallbackonthetheoriesaboutthehumanmindandbasichumanneeds.One,setforthbyAristotleinthecenturyB.C.,seeshumansasnaturallyimitative—astakingpleasureinimitatings,things,andactionsandinseeingsuchimitations.Another,advancedinthetwentiethcentury,suggeststhathumanshaveagiftforfantasy,throughwhichtheyseektoreshaperealityintomoresatisfyingformsthanthoseencounteredindailylife.Thus,fantasyorfiction(ofwhichdramaisoneform)permitspeopletoobjectifytheiranxietiesandfears,confrontthem,andfulfilltheirhopesinfictionifnotfact.Thetheater,then,isonetoolwherebypeopledefineandunderstandtheirworldorescapefromunpleasantrealities. Butneitherthehumanimitativeinstinctnorapenchantforfantasybyitselfleadstoanautonomoustheater.Therefore,additionalexnationsareneeded.Onenecessaryconditionseemstobeasomewhatdetachedviewofhumanproblems.Forexample,onesignofthisconditionistheappearanceofthecomicvision,sincecomedyrequiressufficientdetaenttoviewsomedeviationsfromsocialnormsasridiculousratherthanasseriousthreatstothewelfareoftheentiregroup.Anotherconditionthatcontributestothedevelopmentofautonomoustheateristheemergenceoftheaestheticsense.Forexample,someearlysocietiesceasedtoconsidercertainritesessentialtotheirwell-beingandabandonedthem,nevertheless,theyretainedaspartsoftheiroraltraditionthemythsthathadgrownuparoundtheritesand admiredthemfortheir

qualitiesratherthanfortheirseekadv.首要drawadv.廣泛adj.令人滿adv.簡短adv.頻繁adj.有魔力n.偉大的功act把…表演adv.從那adv.漸漸 rebynocomedetaadv.自然adj.模仿性adj.令人滿fallbacksetiftakepleasureadj.讓人不adj.【Passage1Inseekingtodescribetheoriginsoftheater,onemustrelyprimarilyonspeculation,sincethereislittleconcreteevidenceonwhichtodraw.①Themostwidelyacceptedtheory,championedbyanthropologistsinthelatenineteenthandearlytwentiethcenturies,envisionstheaterasemergingoutofmythandritual.Theprocessperceivedbytheseanthropologistsmaybesummarizedbriefly.Duringtheearlystagesofitsdevelopment,asociety esawareofsthatappeartoinfluenceorcontrolitsfoodsupplyandwell-being.②Havinglittleunderstandingofnaturalcauses,itattributesbothdesirableandundesirableoccurrencestosupernaturalormagicals,anditsearchesformeanstowinthefavoroftheses.Perceivinganapparentconnectionbetweencertainactionsperformedbythegroupandtheresultitdesires,thegrouprepeats,refinesandformalizesthoseactionsintofixedceremonies,orrituals.請用橫 畫出句子主種理論得到了世人的廣泛認同，這種觀點認為戲劇于神話和儀式。請用橫 畫出句子主AttributingAtoB，AB【Passage2Stories(myths)maythengrowuparoundaritual.Frequentlythemythsincluderepresentativesofthosesupernaturalsthattheritescelebrateorhopetoinfluence.③Performersmaywearcostumesandmaskstorepresentthemythicalcharactersorsupernaturalsintheritualsorinpanyingcelebrations.Asapeople esmoresophisticated,itsconceptionsofsupernaturalsandcausalrelationshipsmaychange.Asaresult,itmayabandonormodifysomerites.④Butthemythsthathavegrownuparoundtheritesmaycontinueaspartofthegroup’soraltraditionandmayevencometobeactedoutunderconditionsdivorcedfromtheserites.Whenthisoccurs,thefirststephasbeentakentowardtheaterasanautonomousactivity,andthereafterentertainmentandaestheticvaluesmaygraduallyrecetheformermysticalandsociallyefficaciousconcerns.請用橫 畫出句子主第一個or連接的成分是Mythicalcharacters和supernaturals,第二個or連接的成分是intherituals和 panyingcelebrations.請用橫 畫出句子主maycontinuecometobeacted 【Passage3⑤Althoughorigininritualhaslongbeenthemostpopular,itisbynomeanstheonlytheoryabouthowthetheatercameintobeing.Storylinghasbeenproposedasonealternative.Underthistheory,relatingandlisteningtostoriesareseenasfundamentalhumanpleasures.⑥Thus,therecallingofanevent(ahunt,battle,orotherfeat)iselaboratedthroughthenarrator’spantomimeandim ationandeventuallythrougheachrolebeingassumedbyadifferent 請用橫 畫出句子主itoriginin 請用橫 句中andpantomime ation，第二個and連接的成分是throughthenarrator’spantomimeandim ation和througheachrolebeingassumedbyadifferent【Passage4請用橫 畫出句子主orpantomimicrhythmicalgymnasticoroutofdancesimitationsofanimalnoisesandsounds⑦Acloselyrelated請用橫 畫出句子主orpantomimicrhythmicalgymnasticoroutofdancesimitationsofanimalnoisesandsounds3.翻譯：另一種與之相關的理論認為，戲劇主要是從無聲的、有節(jié)奏的舞蹈體操或者是對動 模仿中逐漸演變而來的【Passage5Inadditiontoexploringthepossibleantecedentsoftheater,scholarshavealsotheorizedaboutthemotivesthatledpeopletodeveloptheater.Whydidtheaterdevelop,andwhywasitvaluedafteritceasedtofulfillthefunctionofritual?Mostanswersfallbackonthetheoriesaboutthehumanmindandbasichumanneeds.⑧One,setforthbyAristotleinthecenturyB.C.,seeshumansasnaturallyimitative—astakingpleasureinimitating s,things,andactionsandinseeingsuchimitations.Another,advancedinthetwentiethcentury,suggeststhathumanshaveagiftforfantasy,throughwhichtheyseektoreshaperealityintomoresatisfyingformsthanthoseencounteredindailylife.Thus,fantasyorfiction(ofwhichdramaisoneform)permitspeopletoobjectifytheiranxietiesandfears,confrontthem,andfulfilltheirhopesinfictionifnotfact.Thetheater,then,isonetoolwherebypeopledefineandunderstandtheirworldorescapefromunpleasantrealities.請用橫 畫出句子主setforth這一句在句子中的成分是非限制性定語從句，其先行詞是one第一個and連接的成分是 第二個and連接的成分是inimitating s,things,andactions和inseeingsuchimitations翻譯在公元前4世紀提出，人們天生好模仿，并且從模仿他人、事物和動作以及模仿中獲得樂趣。：【Passage6：Butneitherthehumanimitativeinstinctnorapenchantforfantasybyitselfleadstoanautonomoustheater.Therefore,additionalexnationsareneeded.Onenecessaryconditionseemstobeasomewhatdetachedviewofhumanproblems.9Forexample,onesignofthisconditionistheappearanceofthecomicvision,sincecomedyrequiressufficientdetaenttoviewsomedeviationsfromsocialnormsasridiculousratherthanasseriousthreatstothewelfareoftheentiregroup.Anotherconditionthatcontributestothedevelopmentofautonomoustheateristheemergenceoftheaestheticsense.Forexample,someearlysocietiesceasedtoconsidercertainritesessentialtotheirwell-beingandabandonedthem,nevertheless,theyretainedaspartsoftheiroraltraditionthemythsthathadgrownuparoundtheritesandadmiredthemfortheiricqualitiesratherthanfortheirreligious請用橫 畫出句子主apperancesincedeviationsfromsocialnorms視為荒謬可笑的，而不認為其會對整個社會群體的福利產生嚴重TPO1-TimberlineVegetationonMountainsThetransitionfromtotreelesstundraonamountainslopeoftenadramaticone.Withinaverticaldistanceofjustafewtensofmeters,treesdisappearasalife-formandarerecedbylowshrubs,herbs,andgrasses.Thisrapidzoneoftransitioniscalledtheuppertimberlineortreeline.Inmanysemiaridareasthereisalsoalowertimberlinewherethepassesintosteppeordesertatitsloweredge,usuallybecauseofalackofmoisture.Theuppertimberline,likethesnowline,ishighestinthetropicandlowestinthepolarregions.Itrangesfromsealevelinthepolarregionsto4,500metersinthedrysubtropicsand3,500–4,500metersinthemoisttropics.Timberlinetreesarenormallyevergreens,suggestingthatthesehavesomeadvantageoverdeciduoustrees(thosethatlosetheirleaves)intheextremeenvironmentsoftheuppertimberline.Therearesomeareas,however,wherebroadleafdeciduoustreesformthetimberline.Speciesofbirch,forexample,mayoccuratthetimberlineinpartsoftheHimalayas.Attheuppertimberlinethetreesbeginto etwistedanddeformed.Thisisparticularlytruefortreesinthemiddleandupperlatitudes,whichtendtoattaingreaterheightsonridges,whereasinthetropicsthetreesreachtheirgreaterheightsinthevalleys.Thisisbecausemiddle-andupper-latitudetimberlinesarestronglyinfluencedbythedurationanddepthofthesnowcover.Asthesnowisdeeperandlastslongerinthevalleys,treestendtoattaingreaterheightsontheridges,eventhoughtheyaremoreexposedtohigh-velocitywindsandpoor,thinsoilsthere.Inthetropics,thevalleysappeartobemorefavorablebecausetheyarelesspronetodryout,theyhavelessfrost,andtheyhavedeeperThereisstillnouniversallyagreed-onexnationforwhyshouldbesuchadramaticcessationoftreegrowthattheuppertimberline.Variousenvironmentalfactorsmayyarole.Toomuchsnow,forexample,cansmothertrees,andavalanchesandsnowcreepcandamageordestroythem.Late-lyingsnowreducestheeffectivegrowingseasontothepointwhereseedlingscannotestablishthemselves.Windvelocityalsoincreaseswithaltitudeandmaycauseseriousstressfortrees,asismadeevidentbythedeformedshapesathighaltitudes.Somescientistshaveproposedthatthepresenceofincreasinglevelsofultravioletlightwithelevationmayyarole,whilebrowsingandgrazinganimalsliketheibexmaybeanothercontributingfactor.Probablythemostimportantenvironmentalfactoristemperature,forifthegrowingseasonistooshortandtemperaturesaretoolow,treeshootsandbudscannotmaturesufficientlytosurvivethewintermonths.AbovethetreelinethereiszonethatisgenerallycalledalpineImmediayadjacenttothetimberline,thetundraconsistsofafairlycompletecoveroflow-lyingshrubs,herbs,andgrasses,whilehigherupthenumberanddiversityofspeciesdecreaseuntilthereismuchbaregroundwithoccasionalmossesandlichensandsomeprostratecushionnts.Somentscanevensurviveinfavorablemicrohabitatsabovethesnowline.Thehighestntsintheworldoccurataround6,100metersonMakaluintheHimalayas.Atthisgreatheight,rocks,warmedbythesun,meltsmallsnowdrifts.Themoststrikingcharacteristicofthentsofthealpinezonetheirlowgrowthform.Thisenablesthemtoavoidtheworstrigorsofhighwindsandpermitsthemtomakeuseofthehighertemperaturesimmediayadjacenttothegroundsurface.Inanareawherelowtemperaturesarelimitingtolife,theimportanceoftheadditionalheatnearthesurfaceiscrucial.Thelowgrowthformcanalsopermitthentstotakeadvantageoftheinsulationprovidedbyawintersnowcover.Intheequatorialmountainsthelowgrowthformislessprevalent.readj..在…內）seasnow ya consist堆n.【Passage1Thetransitionfromtotreelesstundraonamountainslopeisoftenadramaticone.①Withinaverticaldistanceofjustafewtensofmeters,treesdisappearasalife-formandarerecedbylowshrubs,herbs,andgrasses.Thisrapidzoneoftransitioniscalledtheuppertimberlineortreeline.②Inmanysemiaridareasthereisalsoalowertimberlinewherethepassesintosteppeordesertatitsloweredge,usuallybecauseofalackofmoisture.11.用橫 句子中并列的謂語是：disappear和arere翻譯在僅僅幾十米的垂直距離內樹木這種生命形式 了2用橫 Wherebecauseof【Passage2Theuppertimberline,likethesnowline,ishighestinthetropicandlowestinthepolarregions.Itrangesfromsealevelinthepolarregionsto4,500metersinthedrysubtropicsand3,500–4,500metersinthemoisttropics.③Timberlinetreesarenormallyevergreens,suggestingthatthesehavesomeadvantageoverdeciduoustrees(thosethatlosetheirleaves)intheextremeenvironmentsoftheuppertimberline.Therearesomeareas,however,wherebroadleafdeciduoustreesformthetimberline.Speciesofbirch,forexample,mayoccuratthetimberlineinpartsoftheHimalayas.3用橫 Suggestingthese9.【Passage3Attheuppertimberlinethetreesbeginto etwistedanddeformed.④Thisisparticularlytruefortreesinthemiddleandupperlatitudes,whichtendtoattaingreaterheightsonridges,whereasinthetropicsthetreesreachtheirgreaterheightsinthevalleys.Thisisbecausemiddle-andupper-latitudetimberlinesarestronglyinfluencedbythedurationanddepthofthesnowcover.Asthesnowisdeeperandlastslongerinthevalleys,treestendtoattaingreaterheightsontheridges,eventhoughtheyaremoreexposedtotheyarelesspronetodryout,theylessfrost,andtheytheyarelesspronetodryout,theylessfrost,andtheyhavedeeper4用橫 which引導的從句類型是非限制性定語從句，其先行詞是whereas5用橫 【Passage4Thereisstillnouniversallyagreed-onexnationforwhythereshouldbesuchadramaticcessationoftreegrowthattheuppertimberline.Variousenvironmentalfactorsmayyarole.Toomuchsnow,forexample,cansmothertrees,andavalanchesandsnowcreepcandamageordestroythem.Late-lyingsnowreducestheeffectivegrowingseasontothepointwhereseedlingscannotestablishthemselves.⑥Windvelocityalsoincreaseswithaltitudeandmaycauseseriousstressfortrees,asismadeevidentbythedeformedshapesathighaltitudes.Somescientistshaveproposedthatthepresenceofincreasinglevelsofultravioletlightwithelevationmayyarole,whilebrowsingandgrazinganimalsliketheibexmaybeanothercontributingfactor.Probablythemostimportantenvironmentalfactoristemperature,forifthegrowingseasonistooshortandtemperaturesaretoolow,treeshootsandbudscannotmaturesufficientlytosurvivethewintermonths.6用橫 increasesmaymadeevidentby【Passage5Abovethetreelinethereiszonethatisgenerallycalledalpine⑦Immediayadjacenttothetimberline,thetundraconsistsofafairlycompletecoveroflow-lyingshrubs,herbs,andgrasses,whilehigherupthenumberanddiversityofspeciesdecreaseuntilthereismuchbaregroundwithoccasionalmossesandlichensandsomeprostratecushion nts.Somentscanevensurviveinfavorablemicrohabitatsabovethesnowline.Thehighestntsintheworldoccurataround6,100metersonMakaluintheHimalayas.Atthisgreatheight,rocks,warmedbythesun,meltsmall7用橫 whiletundranumberand【Passage6Themoststrikingcharacteristicofthentsofthealpinezoneistheirlowgrowthform.Thisenablesthemtoavoidtheworstrigorsofhighwindsandpermitsthemtomakeuseofthehighertemperaturesimmediayadjacenttothegroundsurface.Inanareawherelowtemperaturesarelimitingtolife,theimportanceoftheadditionalheatnearthesurfaceiscrucial.Thelowgrowthformcanalsopermitthentstotakeadvantageoftheinsulationprovidedbyawintersnowcover.Intheequatorialmountainsthelowgrowthformislessprevalent.TPO2-Desert Thedeserts,whichalready aofthe landsurface,haveinrecentdecadesbeenincreasingatanalarmingpace.Theexpansionofdesert-likeconditionsintoareaswheretheydidnotpreviouslyexistiscalleddesertification.Ithasbeenestimatedthatanadditionalone-oftheEarth'slandsurfaceisthreatenedbythis Desertificationis plishedprimarilythroughthelossofstabilizingnaturalvegetationandthesubsequentacceleratederosionofthesoilby andwater.Insomecasestheloosesoilis away,leavingstonysurface.Inothercases,thefinerparticlesmayberemo