最新完整托福模拟题阅读

1最新完整托福模拟题阅读(一)Questions12-20TheelementsotherthanhydrogenandheliumexistInsuchsmallquantitiesthatitisaccuratetosaythattheuniversesomewhatmorethan25percentheliumbyweightandsomewhatlessthan25percenthydrogen.AstronomershQuestions12-20TheelementsotherthanhydrogenandheliumexistInsuchsmallquantitiesthatitisaccuratetosaythattheuniversesomewhatmorethan25percentheliumbyweightandsomewhatlessthan25percenthydrogen.Astronomershavemeasuredtheabundanceofheliumthroughoutourgalaxyandinothergalaxiesaswell.HeliumhasbeenfoundInoldstars,inrelativelyyoungones,ininterstellargas,andinthedistantobjectsknownasquasars.Heliumnucleihavealsobeenfoundtobeconstituentsofcosmicraysthatfallontheearth(cosmicraysarenotreallyaformofradiation;theyconsistofrapidlymovingparticlesofnumerousdifferentkinds).Itdoesn'tseemtomakeverymuchdifferencewheretheheliumisfound.Itsrelativeabundanceneverseemstovarymuch.Insomeplaces,theremaybeslightlymoreofit;Inothers,slightlyless,buttheratioofheliumtohydrogennucleialwaysremainsaboutthesame.Heliumiscreatedinstars.Infact,nuclearreactionsthatconverthydrogentoheliumareresponsibleformostoftheenergythatstarsproduce.However,theamountofheliumthatcouldhavebeenproducedinthismannercanbecalculated,anditturnsouttobenomorethanafewpercent.Theuniversehasnotexistedlongenoughforthisfiguretohesignificantlygreater.Consequently,iftheuniverseissomewhatmorethan25percentheliumnow,thenitmusthavebeenabout25percentheliumatatimenearthebeginning..However,whentheuniversewaslessthanoneminuteold,noheliumcouldhaveexisted.Calculationsindicatethatbeforethistimetemperaturesweretoohighandparticlesofmatterweremovingaroundmuchtoorapidly.Itwasonlyaftertheone-minutepointthatheliumcouldexist.Bythistime,theuniversehadcooledsufficientlythatneutronsandprotonscouldsticktogether.Butthenuclearreactionsthatledtotheformationofheliumwentonforonlyarelativelyshorttime.Bythetimetheuniversewasafewminutesold,heliumproductionhadeffectivelyceased.212.whatdoesthepassagemainlyexplain?(A)Howstarsproduceenergy(B)Thedifferencebetweenheliumandhydrogen(C)Whenmostoftheheliumintheuniversewasformed(D)Whyhydrogenisabundant13.Accordingtothepassage,heliumis(A)thesecond-mostabundantelementintheuniverse(B)difficulttodetect(C)theoldestelementintheuniverse(D)themostprevalentelementinquasars14.Thewordconstituentsinline7isclosestinmeaningto(A)relatives(B)causes(C)components(D)targets15.Whydoestheauthormentioncosmicrays't'inline7?(A)Aspartofalistofthingscontaininghelium(B)Asanexampleofanunsolvedastronomicalpuzzle(C)Toexplainhowtheuniversebegan(D)Toexplaintheabundanceofhydrogenintheuniverse16.Thewordvaryinline10isclosestillmeaningto(A)mean(B)stretch(C)change(D)include17.Thecreationofheliumwithinstars(A)cannotbemeasured(B)producesenergy3(C)produceshydrogenasaby-product(D)causesheliumtobemuchmoreabundantInoldstarsthanInyoungstar:18.Thewordcalculatedinline15isclosestinmeaningto(A)ignored(B)converted(C)increased(D)determined19.Mostoftheheliumintheuniversewasformed(A)ininterstellarspace(B)inaveryshorttime(C)duringthefirstminuteoftheuniverse'sexistence(D)beforemostofthehydrogen20.Thewordceasedinline26isclosestinmeaningto(A)extended(B)performed(C)takenhold(D)stoppedHormonesintheBodyUptothebeginningofthetwentiethcentury,thenervoussystemwasthoughttocontrolallcommunicationwithinthebodyandtheresultingintegrationofbehavior.Scientistshaddeterminedthatnervesran,essentially,onelectricalimpulses.Theseimpulseswerethoughttobetheengineforthought,emotion,movement,andinternalprocessessuchasdigestion.However,experimentsbyWilliamBaylissandErnestStarlingonthechemicalsecretin,whichisproducedinthesmallintestinewhenfoodentersthestomach,eventuallychallengedthatview.Fromthesmallintestine,secretintravelsthroughthebloodstreamtothepancreas.There,itstimulatesthereleaseofdigestivechemicals.Inthisfashion,theintestinalcellsthatproducesecretinultimatelyregulatetheproductionofdifferentchemicalsinadifferentorgan,thepancreas.Suchacoordinationofprocesseshadbeenthoughttorequirecontrolbythenervoussystem;BaylissandStarlingshowedthatitcouldoccurthroughchemicalsalone.ThisdiscoveryspurredStarlingtocointhetermhormonetorefertosecretin,4takingitfromtheGreekwordhormon,meaning“toexcite”or“tosetinmotion.”Ahormoneisachemicalproducedbyonetissuetomakethingshappenelsewhere.Asmorehormoneswerediscovered,theywerecategorized,primarilyaccordingtotheprocessbywhichtheyoperatedonthebody.Someglands(whichmakeuptheendocrinesystem)secretehormonesdirectlyintothebloodstream.Suchglandsincludethethyroidandthepituitary.Theexocrinesystemconsistsoforgansandglandsthatproducesubstancesthatareusedoutsidethebloodstream,primarilyfordigestion.Thepancreasisonesuchorgan,althoughitsecretessomechemicalsintothebloodandthusisalsopartoftheendocrinesystem.Muchhasbeenlearnedabouthormonessincetheirdiscovery.Someplaysuchkeyrolesinregulatingbodilyprocessesorbehaviorthattheirabsencewouldcauseimmediatedeath.Themostabundanthormoneshaveeffectsthatarelessobviouslyurgentbutcanbemorefar-reachinganddifficulttotrack:Theymodifymoodsandaffecthumanbehavior,evensomebehaviorwenormallythinkofasvolun