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精选400句托福阅读长难句(OG&TPO)第一类1.Thesamethinghappenstothisday,thoughonasmallerscale,whereverasediment-ladenriverorstreamemergesfromamountainvalleyontorelativelyflatland,droppingitsloadasthecurrentslows:thewaterusuallyspreadsoutfanwise,depositingthesedimentintheformofasmooth,fan-shapedslope.2.Inlowlandcountryalmostanyspotonthegroundmayoverliewhatwasoncethebedofariverthathassincebecomeburiedbysoil;iftheyarenowbelowthewater’suppersurface(thewatertable),thegravelsandsandsoftheformerriverbed,anditssandbars,willbesaturatedwithgroundwater.3.Butnotethatporosityisnotthesameaspermeability,whichmeasurestheeasewithwhichwatercanflowthroughamaterial;thisdependsonthesizesoftheindividualcavitiesandthecreviceslinkingthem.4.Iftheporesarelarge,thewaterinthemwillexistasdropstooheavyforsurfacetensiontohold,anditwilldrainaway;butiftheporesaresmallenough,thewaterinthemwillexistasthinfilms,toolighttoovercometheforceofsurfacetensionholdingtheminplace;thenthewaterwillbefirmlyheld.5.Butthemythsthathavegrownuparoundtheritesmaycontinueaspartofthegroup’soraltraditionandmayevencometobeactedoutunderconditionsdivorcedfromtheserites.6.Another,advancedinthetwentiethcentury,suggeststhathumanshaveagiftforfantasy,throughwhichtheyseektoreshaperealityintomoresatisfyingformsthanthoseencounteredindailylife.7.Forexample,onesignofthisconditionistheappearanceofthecomicvision,sincecomedyrequiressufficientdetachmenttoviewsomedeviationsfromsocialnormsasridiculousratherthanasseriousthreatstothewelfareoftheentiregroup.8.Timberlinetreesarenormallyevergreens,suggestingthatthesehavesomeadvantageoverdeciduoustrees(thosethatlosetheirleaves)intheextremeenvironmentsoftheuppertimberline.9.Thisisparticularlytruefortreesinthemiddleandupperlatitudes,whichtendtoattaingreaterheightsonridges,whereasinthetropicsthetreesreachtheirgreaterheightsinthevalleys.10.Asthesnowisdeeperandlastslongerinthevalleys,treestendtoattaingreaterheightsontheridges,eventhoughtheyaremoreexposedtohigh-velocitywindsandpoor,thinsoilsthere.11.Windvelocityalsoincreaseswithaltitudeandmaycauseseriousstressfortrees,asismadeevidentbythedeformedshapesathighaltitudes.12.Somescientistshaveproposedthatthepresenceofincreasinglevelsofultravioletlightwithelevationmayplayarole,whilebrowsingandgrazinganimalsliketheibexmaybeanothercontributingfactor.13.Probablythemostimportantenvironmentalfactoristemperature,forifthegrowingseasonistooshortandtemperaturesaretoolow,treeshootsandbudscannotmaturesufficientlytosurvivethewintermonths.14.Immediatelyadjacenttothetimberline,thetundraconsistsofafairlycompletecoveroflow-lyingshrubs,herbs,andgrasses,whilehigherupthenumberanddiversityofspeciesdecreaseuntilthereismuchbaregroundwithoccasionalmossesandlichensandsomeprostratecushionplants.15.Inorderforthestructuretoachievethesizeandstrengthnecessarytomeetitspurpose,architectureemploysmethodsofsupportthat,becausetheyarebasedonphysicallaws,havechangedlittlesincepeoplefirstdiscoveredthem-evenwhilebuildingmaterialshavechangeddramatically.16.Someoftheworld’sfineststonearchitecturecanbeseenintheruinsoftheancientIncacityofMachuPicchuhighintheeasternAndesMountainsofPeru.17.Itworksincompressiontodiverttheweightaboveitouttothesides,wheretheweightisbornebytheverticalelementsoneithersideofthearch.18.TheOgallalaaquiferisasandstoneformationthatunderliessome583,000squarekilometersoflandextendingfromnorthwesternTexastosouthernSouthDakota.19.Unfortunately,thecostofwaterobtainedthroughanyoftheseschemeswouldincreasepumpingcostsatleasttenfold,makingthecostofirrigatedagriculturalproductsfromtheregionuncompetitiveonthenationalandinternationalmarkets.20.Whateverthefinalanswertothewatercrisismaybe,itisevidentthatwithintheHighPlains,irrigationwaterwillneveragainbetheabundant,inexpensiveresourceitwasduringtheagriculturalboomyearsofthemid-twentiethcentury.21.Totakeanextremeexample,farmlandsdominatedbyasinglecroparesounstablethatoneyearofbadweatherortheinvasionofasinglepestcandestroytheentirecrop.22.Ecologistsareespeciallyinterestedtoknowwhatfactorscontributetotheresilienceofcommunitiesbecauseclimaxcommunitiesallovertheworldarebeingseverelydamagedordestroyedbyhumanactivities.23.ThedestructioncausedbythevolcanicexplosionofMountSt.Helens,inthenorthwesternUnitedStates,forexample,palesincomparisontothedestructioncausedbyhumans.24.Manyecologistsnowthinkthattherelativelong-termstabilityofclimaxcommunitiescomesnotfromdiversitybutfromthe“patchiness”oftheenvironment,anenvironmentthatvariesfromplacetoplacesupportsmorekindsoforganismsthananenvironmentthatisuniform.25.Similarly,aplantoranimalcannotsquanderallitsenergyongrowingabigbodyifnonewouldbeleftoverforreproduction,forthisisthesurestwaytoextinction.26.Attheotherextremeare“competitors,”almostallofwhoseresourcesareinvestedinbuildingahugebody,withabareminimumallocatedtoreproduction.27.Anewplantwillspringupwhereveraseedfallsonasuitablesoilsurface,butbecausetheydonotbuildbigbodies,theycannotcompetewithotherplantsforspace,water,orsunlight.28.Theseplantsaretermedopportunistsbecausetheyrelyontheirseeds’fallingintosettingswherec