人教版英语必修3 unit4-5课本电子版

人教版英语必修3unit4--5课本电子版人教版英语必修3unit4--5课本电子版人教版英语必修3unit4--5课本电子版资料仅供参考文件编号：2022年4月人教版英语必修3unit4--5课本电子版版本号：A修改号：1页次：1.0审核：批准:发布日期：HOWLIFEBEGANONTHEEARTHNooneknowsexactlyhowtheearthbegan,asithappenedsolongago.However,accordingtoawidelyacceptedtheory,theuniversebeganwitha"BigBang"thatthrewmatterinalldirections.Afterthat,atomsbegantoformandcombinetocreatestarsandotherbodies.Forseveralbillionyearsafterthe"BigBang",theearthwasstilljustacloudofdust.Whatitwastobecomewasuncertainuntilbetween4.5and3.8billionyearsagowhenthedustsettledintoasolidglobe.Theearthbecamesoviolentthatitwasnotclearwhethertheshapewouldlastornot.Itexplodedloudlywithfireandrock.Theywereintimetoproducecarbon,nitrogen,watervapourandothergases,whichweretomaketheearth'satmosphere.Whatisevenmoreimportantisthatastheearthcooleddown,waterbegantoappearonitssurface.WaterhadalsoappearedonotherplanetslikeMarsbut,unliketheearth,ithaddisappearedlater.Itwasnotimmediatelyobviousthatwaterwastobefundamentaltothedevelopmentoflife.Whatmanyscientistsbelieveisthatthecontinuedpresenceofwaterallowedtheearthtodissolveharmfulgasesandacidsintotheoceansandseas.Thisproducedachainreaction,whichmadeitpossibleforlifetodevelop.Manymillionsofyearslater,thefirstextremelysmallplantsbegantoappearonthesurfaceofthewater.Theymultipliedandfilledtheoceansandseaswithoxygen,whichencouragedthelaterdevelopmentofearlyshellfishandallsortsoffish.Next,greenplantsbegantogrowonland.Theywerefollowedintimebylandanimals.Somewereinsects.Others,calledamphibians,wereabletoliveonlandaswellasinthewater.Laterwhentheplantsgrewintoforests,reptilesappearedforthefirsttime.Theyproducedyounggenerallybylayingeggs.Afterthat,somehugeanimals,calleddinosaurs,developed.Theylaideggstooandexistedontheearthformorethan140millionyears.However,65millionyearsagotheageofthedinosaursended.Whytheysuddenlydisappearedstillremainsamystery.Thisdisappearancemadepossibletheriseofmammalsontheearth.Theseanimalsweredifferentfromalllifeformsinthepast,becausetheygavebirthtoyoungbabyanimalsandproducedmilktofeedthem.Finallyabout2.6millionyearsagosomesmallcleveranimals,nowwithhandsandfeet,appearedandspreadallovertheearth.Thustheyhave,intheirturn,becomethemostimportantanimalsontheplanet.Buttheyarenotlookingaftertheearthverywell.Theyareputtingtoomuchcarbondioxideintotheatmosphere,whichpreventsheatfromescapingfromtheearthintospace.Asaresultofthis,manyscientistsbelievetheearthmaybecometoohottoliveon.Sowhetherlifewillcontinueontheearthformillionsofyearstocomewilldependonwhetherthisproblemcanbesolved.AVISITTOTHEMOONLastmonthIwasluckyenoughtohaveachancetomakeatripintospacewithmyfriendLiYanping,anastronomer.Wevisitedthemooninourspaceship!Beforeweleft,LiYanpingexplainedtomethattheforceofgravitywouldchangethreetimesonourjourneyandthatthefirstchangewouldbethemostpowerful.Thenwewereoff.Astherocketroseintotheair,wewerepushedbackintoourseatsbecauseweweretryingtoescapethepulloftheearth'sgravity.Itwassohardthatwecouldnotsayanythingtoeachother.GraduallytheweightlessenedandIwasabletotalktohim."Whyisthespaceshipnotfallingbacktotheearth

OntheearthifIfallfromatreeIwillfalltotheground."Iasked."Wearetoofarfromtheearthnowtofeelitspull,"heexplained,"sowefeelasifthereisnogravityatall.Whenwegetclosertothemoon,weshallfeelitsgravitypullingus,butitwillnotbeasstrongapullastheearth's."Icheeredupimmediatelyandfloatedweightlesslyaroundinourspaceshipcabinwatchingtheearthbecomesmallerandthemoonlarger.Whenwegotthere,Iwantedtoexploreimmediately."Comeon,"Isaid."Ifyouareright,mymasswillbelessthanontheearthbecausethemoonissmallerandIwillbeabletomovemorefreely.ImightevengrowtallerifIstayherelongenough.Ishallcertainlyweighless!"Ilaughedandclimbeddownthestepsfromthespaceship.ButwhenItriedtostepforward,IfoundIwascarriedtwiceasfarasontheearthandfellover."Ohdear,"Icried,"walkingdoesneedabitofpracticenowthatgravityhaschanged."AfterawhileIgotthehangofitandwebegantoenjoyourselves.Leavingthemoon'sgravitywasnotaspainfulasleavingtheearth's.Butreturningtotheearthwasveryfrightening.Wewatched,amazedasfirebrokeoutontheoutsideofthespaceshipastheearth'sgravityincreased.Againwewerepushedhardintoourseatsaswecamebacktoland."Thatwasveryexhaustingbutveryexcitingtoo,"Isaid."NowIknowmuchmoreaboutgravity!Doyouthinkwecouldvisitsomestarsnexttime""Ofcourse,"hesmiled,"whichstarwouldyouliketogoto"CAUGHTBYABLACKHOLEThespaceshipwarnedLiYanpingandmetobereadyaswewereapproachingthe"blackhole".Wecouldseesomefaintlightsaroundwhatlookedlikeanemptyspace.LiYanpingsaid,"Thatemptyholeislikeamouthalwaysneedingtobefed.Thoselightsarethingsthatarebeingpulledintoitbythegravityofthehole."Wewatchedwithinterestandamazementatthelightswhichseemedtobegoingfainterandfainterroundtheedgeoftheblackhole.Justthenthelightsonourspaceshipwentoutandthecomputerstoppedworking.WhatwashappeningItriedtoturnthespaceshipawayfromtheholebutitwouldnotmove.Woulditeatustoo

Suddenlythespaceshipjumpedandbegantomoveroundtheedgeoftheholetoo.Thegravityofthe"blackhole"waspullingusintoits"mouth".Asthespaceshipmovedroundtheblackhole,Ifeltrathersick.MymouthwentdryandIclosedmyeyes.Allthestoriesaboutwhathappenedwhenyouwerecaughtbythegravityofa"blackhole"seemedtobetrue.Butthenthespaceshipjumpedagain.Thistimeitmovedsidewaysandawayfromtheedgeofthe"blackhole".Someonewatchingmewouldhaveseenthespaceshipflyinglikeabirdawayfromthe"blackhole".Butwefeltnothing.Atlastwewereabletolookaroundus.Luckilythecomputerhadstartedworkingagain.Werealizedthatwehaddiscoveredsomethingnewabout"blackholes".Ifyougoinsidetheedgeofa"blackhole",itwill"eat"youandthereisnoescape;butifyoudonot,youmayhaveanopportunitytoescape.Howexciting!Unit5ATRIPON"THETRUENORTH"LiDaiyuandhercousinLiuQianwereonatriptoCanadatovisittheircousinsinMontrealontheAtlanticcoast.Ratherthantaketheaeroplanealltheway,theydecidedtoflytoVancouverandthentakethetrainwesttoeastacrossCanada.Thethoughtthattheycouldcrossthewholecontinentwasexciting.Theirfriend,DannyLin,waswaitingattheairport.Hewasgoingtotakethemandtheirbaggagetocatch"TheTrueNorth",thecross-Canadatrain.Onthewaytothestation,hechattedabouttheirtrip."You'regoingtoseesomegreatscenery.Goingeastward,you'llpassmountainsandthousandsoflakesandforests,aswellaswideriversandlargecities.SomepeoplehavetheideathatyoucancrossCanadainlessthanfivedays,buttheyforgetthefactthatCanadais5,500kilometresfromcoasttocoast.HereinVancouver,you'reinCanada'swarmestpart.PeoplesayitisCanada'smostbeautifulcitysurroundedbymountainsandthePacificOcean.SkiingintheRockyMountainsandsailingintheharbourmakeVancouveroneofCanada'smostpopularcitiestolivein.Itspopulationisincreasingrapidly.ThecoastnorthofVancouverhassomeoftheoldestandmostbeautifulforestsintheworld.Itissowettherethatthetreesareextremelytall,somemeasuringover90metres."Thatafternoonaboardthetrain,thecousinssettleddownintheirseats.Earlierthatday,whentheycrossedtheRockyMountains,theymanagedtocatchsightofsomemountaingoatsandevenagrizzlybearandaneagle.TheirnextstopwasCalgary,whichisfamousfortheCalgaryStampede.CowboysfromallovertheworldcometocompeteintheStampede.Manyofthemhaveagiftforridingwildhorsesandcanwinthousandsofdollarsinprizes.Aftertwodays'travel,thegirlsbegantorealizethatCanadaisquiteempty.Atschool,theyhadlearnedthatmostCanadianslivewithinafewhundredkilometresoftheUSAborder,andCanada'spopulationisonlyslightlyoverthirtymillion,butnowtheywereamazedtoseesuchanemptycountry.Theywentthroughawheat-growingprovinceandsawfarmsthatcoveredthousandsofacres.Afterdinner,theywerebackinanurbanarea,thebusyportcityofThunderBayatthetopoftheGreatLakes.ThegirlsweresurprisedatthefactthatoceanshipscansailuptheGreatLakes.BecauseoftheGreatLakes,theylearned,Canadahasmorefreshwaterthananyothercountryintheworld.Infact,ithasone-thirdoftheworld'stotalfreshwater,andmuchofitisintheGreatLakes.Thatnightastheyslept,thetrainrushedacrossthetopofLakeSuperior,throughthegreatforestsandsouthwardtowardsToronto.“THETURENORTH”FROMTORONTOTOMONTREALThenextmorningthebushesandmapletreesoutsidetheirwindowswerered,goldandorange,andtherewasfrostontheground,confirmingthatfallhadarrivedinCanada.AroundnoontheyarrivedinToronto,thebiggestandmostwealthycityinCanada.TheywerenotleavingforMontrealuntillater,sotheywentonatourofthecity.TheywentupthetallCNTowerandlookedacrossthelake.Inthedistance,theycouldseethemistycloudthatrosefromthegreatNiagaraFalls,whichisonthesouthsideofthelake.ThewaterflowsintotheNiagaraRiverandoverthefallsonitswaytothesea.Theysawthecoveredstadium,homeofseveralfamousbasketballteams.Astheywalkednorthfromtheharbourarea,LiDaiyusaid,"LinFei,oneofmymother'soldschoolmates,liveshere.Ishouldphoneherfromatelephonebooth."TheymetLinFeiaroundduskindowntownChinatown,oneofthethreeinToronto.OverdinneratarestaurantcalledThePinkPearl,thecousinschattedwithLinFei,whohadmovedtoCanadamanyyearsearlier."WecangetgoodCantonesefoodhere,"LinFeitoldthem,"becausemostoftheChinesepeopleherecomefromSouthChina,especiallyHongKong.It'stoobadyoucan'tgoasfarasOttawa,Canada'scapital.It'sapproximatelyfourhundredkilometresnortheastofTorontoThetrainleftlatethatnightandarrivedinMontrealatdawnthenextmorning.Atthestation,peopleeverywherewerespeakingFrench.ThereweresignsandadsinFrench,butsomeofthemhadEnglishwordsinsmallerletters."Wedon'tleaveuntilthisevening,"saidLiuQian."Let'sgodowntown.OldMontrealisclosetothewater."Theyspenttheafternooninlovelyshopsandvisitingartistsintheirworkplacesbesidethewater.AstheysatinabuffetrestaurantlookingoverthebroadStLawrenceRiver"Hello,mynameisHenri.I'mastudentattheuniversitynearby,"hesaid,"andIwaswonderingwhereyouarefrom."ThegirlstoldhimtheywereonatraintripacrossCanadaandthattheyhadonlyonedayinMontreal."That'stoobad,"hesaid."Montrealisacitywithwonderfulrestaurantsandclubs.MostofusspeakbothEnglishandFrench,butthecityhasFrenchcultureandtraditions.Welovegoodcoffee,goodbreadandgoodmusic."ThatnightasthetrainwasspeedingalongtheStLawrenceRivertowardtheGulfofStLawrenceanddowntothedistanteastcoast,thecousinsdreamedofFrenchrestaurantsandredmapleleaves.IQALUIT--THEFROZENTOWNThereporter,BethAllen,arrivedinanortherncommunitycalledIqaluitinNunavut.Nunavutwascreatedin1999asaspecialareaforInuitpeople.Itsnamemeans"OurLand"intheirlanguage.ItisinthefarthestnortheasternareaofCanada,northoftheArcticCircle,andisverycold-theaveragewintertemperatureinNunavutBethsaid,"IknewitwouldbecoldinJanuary,butnotthiscold!Maybethereisadogsledthatcantakemeintotown."Thequietmanwhohadbeenontheplanewithhersaid,"I'lltakeyouintotown,butIdon'thaveadogsled.Mostpeopleonlyusethedogsforcompetitio