大学英语六级考试快速阅读模拟题训练Word下载.docx
《大学英语六级考试快速阅读模拟题训练Word下载.docx》由会员分享,可在线阅读,更多相关《大学英语六级考试快速阅读模拟题训练Word下载.docx(14页珍藏版)》请在冰豆网上搜索。
Y(forYES)ifthestatementagreeswiththeinformationgiveninthepassage;
N(forNO)ifthestatementcontradictstheinformationgiveninthepassage;
NG(forNOTGIVEN)iftheinformationisnotgiveninthepassage.
Forquestions5-10,completethesentenceswiththeinformationgiveninthepassage.
Rainforests
Tropicalrainforestsarethemostdiverseecosystem(生态系统)onEarth,andalsotheoldest.Today,tropicalrainforestscoveronly6percentoftheEarth'
sgroundsurface,buttheyarehometooverhalfoftheplanet'
splantandanimalspecies.
WhatIsaRainforest?
Generallyspeaking,arainforestisanenvironmentthatreceiveshighrainfallandisdominatedbytalltrees.Awiderangeofecosystemsfallintothiscategory,ofcourse.Butmostofthetimewhenpeopletalkaboutrainforests,theymeanthetropicalrainforestslocatedneartheequator.
Theseforestsreceivebetween160and400inchesofrainperyear.Thetotalannualrainfallisspreadprettyevenlythroughouttheyear,andthetemperaturerarelydipsbelow60degreesFahrenheit.
Thissteadyclimateisduetothepositionofrainforestsontheglobe.BecauseoftheorientationoftheEarth'
saxis,theNorthernandSouthernhemisphereseachspendpartoftheyeartiltedawayfromthesun.Sincerainforestsareatthemiddleoftheglobe,locatedneartheequator,theyarenotespeciallyaffectedbythischange.Theyreceivenearlythesameamountofsunlight,andthereforeheat,allyear.Consequently,theweatherintheseregionsremainsfairlyconstant.
Theconsistentlywet,warmweatherandamplesunlightgiveplantlifeeverythingitneedstothrive.Treeshavetheresourcestogrowtotremendousheights.andtheyliveforhundreds,eventhousands,ofyears.Thesegiants,whichreach60to150ftintheair,formthebasicstructureoftherainforest.Theirtopbranchesspreadwideinordertocapturemaximumsunlight.Thiscreatesathickcanopy(树冠)levelatthetopoftheforest,withthinnergreenerylevelsunderneath.Somelargetreesgrowsotallthattheyeventoweroverthecanopylayer.
Asyougolower,downintotherainforest,youfindlessandlessgreenery.Theforestfloorismadeupofmoss,fungi,anddecayingplantmatterthathasfallenfromtheupperlayers.Thereasonforthisdecreaseingreeneryisverysimple:
Theoverabundanceofplantsgatheringsunlightatthetopoftheforestblocksmostsunlightfromreachingthebottomoftheforest,makingitdifficultforrobustplantstothrive.
TheForestfortheTrees
Theamplesunlightandextremelywetclimateofmanytropicalareasencouragethegrowthoftoweringtreeswithwidecanopies.Thisthicktoplayeroftherainforestdictatesthelivesofallotherplantsintheforest.Newtreeseedlingsrarelysurvivetomakeittothetopunlesssomeoldertreesdie,creatinga"
hole"
inthecanopy.Whenthishappens,alloftheseedlingsonthegroundlevelcompeteintenselytoreachthesunlight.
Manyplantspeciesreachthetopoftheforestbyclimbingthetalltrees.Itismucheasiertoascendthisway,becausetheplantdoesn'
thavetoformitsownsupportingstructure.
Someplantspecies,calledepiphytes,growdirectlyonthesurfaceofthegianttrees.Theseplants,whichincludeavarietyoforchidsandferns,makeupmuchoftheunderstory,thelayeroftherainforestrightbelowthecanopy.Epiphytesarecloseenoughtothetoptoreceiveadequatelight,andtherunofffromthecanopylayerprovidesallthewaterandnutrients(养分)theyneed,whichisimportantsincetheydon'
thaveaccesstothenutrientsintheground.
StranglersandButtresses
Someepiphyteseventuallydevelopintostranglers.Theygrowlong,thickrootsthatextenddownthetreetrunkintotheground.Astheycontinuetogrow,therootsformasortofwebstructureallaroundthetree.Atthesametime,thestranglerplant'
sbranchesextendupward,spreadingoutintothecanopy.Eventually,thestranglermayblocksomuchlightfromabove,andabsorbsuchahighpercentageofnutrientsfromthegroundbelow,thatthehosttreedies.
Competitionovernutrientsisalmostasintenseascompetitionforlight.Theexcessiverainfallrapidlydissolvesnutrientsinthesoil,makingitrelativelyinfertileexceptatthetoplayers.Forthisreason,rainforesttreerootsgrowoutwardtocoverawiderarea,ratherthandownwardtolowerlevels.Thismakesrainforesttreessomewhatunstable,sincetheydon'
thaveverystronganchorsintheground.Sometreescompensateforthisbygrowingnaturalbuttresses.Thesebuttressesarebasicallytreetrunksthatextendoutfromthesideofthetreeanddowntotheground,givingthetreeadditionalsupport.
Rainforesttreesaredependentonbacteriathatarecontinuallyproducingnutrientsintheground.Rainforestbacteriaandtreeshaveaveryclose,symbiotic(共生的)relationship.Thetreesprovidethebacteriawithfood,intheformoffallenleavesandothermaterial,andthebacteriabreakthismaterialdownintothenutrientsthatthetreesneedtosurvive.
Oneofthemostremarkablethingsaboutrainforestplantlifeisitsdiversity.ThetemperaterainforestsofthePacificNorthwestaremainlycomposedofadozenorsotreespecies.Atropicalrainforest,ontheotherhand,mighthave300distincttreespecies.
AllCreatures,GreatandSmall
Rainforestsarehometothemajorityofanimalspeciesintheworld.Andagreatnumberofspecieswhonowliveinotherenvironments,includinghumans,originallyinhabitedtherainforests.Researchersestimatethatinalargerainforestarea,theremaybemorethan10milliondifferentanimalspecies.
Mostofthesespecieshaveadaptedforlifeintheupperlevelsoftherainforest,wherefoodismostplentiful.Insects,whichcaneasilyclimborflyfromtreetotree,makeupthelargestgroup(antsarethemostabundantanimalintherainforest).Insectspecieshaveahighlysymbioticrelationshipwiththeplantlifeinarainforest.Theinsectsmovefromplanttoplant,enjoyingthewealthoffoodprovidedthere.Astheytravel,theinsectsmaypickuptheplants'
seeds,droppingthemsomedistanceaway.Thishelpstodispersethepopulationoftheplantspeciesoveralargerarea.
Thenumerousbirdsoftherainforestalsoplayamajorpartinseeddispersal.Whentheyeatfruitfromaplant,theseedspassthroughtheirdigestivesystem.Bythetimetheyexcrete(排泄)theseeds,thebirdsmayhaveflownmanymilesawayfromthefruit-bearingtree.
Therearealsoalargenumberofreptilesandmammalsintherainforest.Sincetheweatherissohotandhumidduringtheday,mostrainforestmammalsareactiveonlyatnight,duskordawn.Themanyrainforestbatspeciesareespeciallywelladaptedforthislifestyle.Usingtheirsonar,batsnavigateeasilythroughthemassoftreesintherainforest,feedingoninsectsandfruit.
Whilemostrainforestspeciesspendtheirlivesinthetrees,thereisalsoalotoflifeontheforestfloor.Greatapes,wildpigs,bigcatsandevenelephantscanallbefoundinrainforests.Thereareanumberofpeoplewholiveintherainforests,aswell.Thesetribes-which,upuntilrecently,numberedinthethousands-arebeingforcedoutoftherainforestsatanalarmingratebecauseofdeforestation.
Deforestation
Inthepasthundredyears,humanshavebegundestroyingrainforestsatanalarmingrate.Today,roughly1.5acresofrainforestaredestroyedeverysecond.Peoplearecuttingdowntherainforestsinpursuitofthreemajorresources:
•Landforcrops
•Lumberforpaperandotherwoodproducts
•Landforlivestockpastures
Inthecurrenteconomy,peopleobviouslyhaveaneedforalloftheseresources.Butalmostallexpertsagreethat,overtime,wewillsuffermuchmorefromthedestructionoftherainforeststhanwewillbenefit.
Theworld'
srainforestsareanextremelyvaluablenaturalresource,tobesure,butnotfortheirlumberortheirland.TheyarethemaincradleoflifeonEarth,andtheyholdmillionsofuniquelifeformsthatwehaveyettodiscover.Destroyingtherainforestsiscomparabletodestroyinganunknownplanet-wehavenoideawhatwe'
relosing.Ifdeforestationcontinuesatitscurrentrate,theworld'
stropicalrainforestswillbewipedoutwithin40years.
1.VirtuallyallplantandanimalspeciesonEarthcanbefoundintropicalrainforests.
2.Thereisnotmuchchangeintheweatherinthetropicalrainforestsalltheyearround.
3.ThelargestnumberofrainforestsintheworldarelocatedontheAfricancontinent.
4.Belowthecanopylevelofatropicalrainforestgrowsanoverabundanceofplants.
5.Newtreeseedlingswillnotsurvivetoreachthecanopylevelunless________.
6.Epiphytes,whichformmuchoftheunderstoryoftherainforest,getalltheirwaterandnutrientsfrom________.
7.Stranglersaresocalledbecausethey________byblockingthesunlightandcompetingforthenutrients.
8.Sincerainforestbacteriaandtreesdependoneachotherforlife,therelationshiptheyformistermed________.
9.Plantspeciesaredispersedoveralargeareawiththehelpof________.
10.Aswearestillignorantofmillionsofuniquelifeformsintherainforest,deforestationcanbecomparedtothedestructionof________.
Unit1
1.N2.Y3.NG4.N
5.guaranteed6.Internetaccess
7.twocustomersatisfactionprograms/acustomerhotlineandacustomercall-backprogram
8.higherpricesoftheirpizzas
9.recklessdrivingbythe