最新完整托福模拟试题阅读

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1、Word格式最新完整托福模拟题阅读(一)Questions12-20TheelementsotherthanhydrogenandheliumexistInsuchsmallquantitiesthatitisaccuratetosaythattheuniversesomewhatmorethan25percentheliumbyweightandsomewhatlessthan25percenthydrogen.AstronomershQuestions12-20　　Theelementsotherthanhyd

2、rogenandheliumexistInsuchsmallquantitiesthatitisaccuratetosaythattheuniversesomewhatmorethan25percentheliumbyweightandsomewhatlessthan25percenthydrogen.　　Astronomershavemeasuredtheabundanceofheliumthroughoutourgalaxyandinothergalaxiesaswell.HeliumhasbeenfoundI

3、noldstars,inrelativelyyoungones,ininterstellargas,andinthedistantobjectsknownasquasars.Heliumnucleihavealsobeenfoundtobeconstituentsofcosmicraysthatfallontheearth(cosmic"rays"arenotreallyaformofradiation;theyconsistofrapidlymovingparticlesofnumerousdifferentki

4、nds).Itdoesn'tseemtomakeverymuchdifferencewheretheheliumisfound.Itsrelativeabundanceneverseemstovarymuch.Insomeplaces,theremaybeslightlymoreofit;Inothers,slightlyless,buttheratioofheliumtohydrogennucleialwaysremainsaboutthesame.　　Heliumiscreatedinstars.Infact,

5、nuclearreactionsthatconverthydrogentoheliumareresponsibleformostoftheenergythatstarsproduce.However,theamountofheliumthatcouldhavebeenproducedinthismannercanbecalculated,anditturnsouttobenomorethanafewpercent.Theuniversehasnotexistedlongenoughforthisfiguretohe

6、significantlygreater.Consequently,iftheuniverseissomewhatmorethan25percentheliumnow,thenitmusthavebeenabout25percentheliumatatimenearthebeginning..　　However,whentheuniversewaslessthanoneminuteold,noheliumcouldhaveexisted.Calculationsindicatethatbeforethistimet

7、emperaturesweretoohighandparticlesofmatterweremoving完美整理Word格式aroundmuchtoorapidly.Itwasonlyaftertheone-minutepointthatheliumcouldexist.Bythistime,theuniv　　ersehadcooledsufficientlythatneutronsandprotonscouldsticktogether.Butthenuclearreactionsthatledtotheform

8、ationofheliumwentonforonlyarelativelyshorttime.Bythetimetheuniversewasafewminutesold,heliumproductionhadeffectivelyceased.　　12.whatdoesthepassagemainlyexplain?　　(A)Howstarsproducee