2012年6月份英语四级标准模拟试题及答案详解

2012年6月份英语四级标准模拟试题及答案详解PartIWriting(30minutes)Directions:Forthispart,youareallowed30minutestowriteacompositiononthetopicToBeCivilizedTourists.Youshouldwriteatleast120wordsfollowingtheoutlinegivenbelowinChinese:1.随着旅游人数增多，游客不文明现象突增2.分析此现象造成的不良影响3.提倡大家做文明游客ToBeCivilizedTourists______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________PartIIReadingComprehension(SkimmingandScanning)(15minutes)Directions:Inthispart,youwillhave15minutestogooverthepassagequicklyandanswerthequestionsonAnswerSheet1.Forquestions1-7,choosethebestanswerfromthefourchoicesmarked[A],[B],[C]and[D].Forquestions8-10,completethesentenceswiththeinformationgiveninthepassage.BiodiversityGenerallyspeaking,thegreatestdegreeofspeciesdiversityisfoundinthewarmtropicalhabitats(thenaturalhomesofplantsoranimals)nearesttheequator.DiversityislowerintheEarth'stemperatezones,andlowestinthepolarregions,aphenomenonknownasthelatitudinalgradient(纬度倾斜度)ofbiodiversity.Andthespeciesrichnessoflandecosystems(生态系统)alsodecreasesathigherelevations.Highamountsofannualrainfallalsocorrelatetoricherdiversityinlandhabitats,withthehighestconcentrationofdifferentspeciesfoundinthetropicalrainforests.Themostdiversemarineecosystemsarelocatedontheocean'scontinentalshelves,althoughdeep-seahabitatsalsodemonstratesignificantspeciesrichness.RainforestsAndCoralReefsSciencehasyettoexplaintheremarkabledegreeofspeciesdiversityfoundintropicalrainforestsandcoralreefs.Theanswerstothisecologicalmysteryinvolveboththeoriginsofdiversitythroughevolutionandthemaintenanceofspeciesdiversity.Tropicalrainforestscoverapproximately9millionsquarekilometers—adecreaseofabout45%sinceman'sarrival.Althoughtheyaccountforonlyabout6%oftheworld'slandsurface,thesehighlydiverseecosystemscontainoverhalfofalllivingspecies.Someresearchersplacethatfigureashighas90%,basedonestimatesofthenumberofmicroorganismsandinsectsbelievedtopopulatetherainforests.Likewise,approximatelyonequarterofmarinespeciesarethoughttoresideontheocean'scoralreefs.Sadly,maniscuttingandburningtheworld'srainforestsatarateofapproximately100,000squarekilometersannually.AsEdwardWilsonexplains,thisamountstothedestructionofanareaofrainforestequaltothesizeofafootballfieldeverysecond.Heconservativelyestimatesthatbetween0.2%and0.3%ofrainforestspecies—thatis4,000to6,000individualspecies—arelosteachyearfromdeforestationalone.Thisis10,000timestherateofnaturalextinctionwhichoccurredbeforehumanintervention.Theproblemissoseverethat,in1990,theindependentScienceAdvisoryBoardoftheU.S.EnvironmentalProtectionAgencynamedhabitatlossandspeciesextinctionastwooftheworld'smostcriticalenvironmentalproblems.ThreatsToBiodiversityThethreatstobiodiversityaremyriad(无数的),butmostarethedirectorindirectresultofhumanactivity.Populationgrowthandmigration,overexploitation,andthelackofsustainableresourceconsumptionpoliciescontinuetostresssensitiveecosystems.SomeofthehighestratesofgrowthareoccurringintheEarth'sspecies-richtropicalregions.Forexample,75millionpeoplealreadyinhabittherainforestsoftheUpperAmazoniaandGuyanaShieldinSouthAmerica,theCongoBasininAfrica,andtheNewGuinea/MelanesianIslandsbetweenAsiaandAustralia,andtheirpopulationsarecontinuingtoexpandatnearly250%oftheworldaverage.Thedestructionofnaturalhabitatstoaccommodatepopulationgrowthandmigrationisthesinglelargestfactorinthelossofspeciesandevenentireecosystems.InthecontinentalUnitedStatesalone,98%ofvirginforestsand51%ofnaturalwetlandshavebeendestroyed.However,lesserhumanintrusions,suchastheremovalofasinglenativepopulationortheintroductionofanon-nativespeciescanalsoseverelydisruptthefunctioningofnaturalecosystems,duetothecomplexnatureoftheirinterrelationshipsandprocesses.Humanactivityalsoproducespollutionandcontaminationwhichcanaffectalllevelsofbiodiversity.Poisonoussubstancesreleasedintoourairandwaternotonlyimpactregionalecosystems,butcanextendtheirharmfuleffectsbeyondstateandnationalborders,asinthecaseofacidrain.Continueddischargeofothersubstancesintotheatmosphere,thoughnotnecessarilypoisonous,leadstotheozonedepletioninthestratosphereandincreasedpenetrationofultravioletradiationtothelandandocean.Scientistshaveidentifiedthe“greenhouseeffects”,whereincreasedlevelsofcarbondioxide,methane,andothergasescaptureheatwithintheEarth'satmosphere.Thisclimaticglobalwarmingisofparticularconcerninthecoldtemperateandpolarregions,wherepossibleclimaticshiftscouldleavebehindentirerangesofplantandanimalspecies.Becauseclimaticchangeswouldbemostseverenearthepoles,entireArcticandAntarcticecosystemscouldbethreatenedwithextinction.Carbonreleasedfromtheburningoff