大学英语自学教程中

大学英语自学教程(中)16-A.HeartDisease:TreatorPrevent?OneofthegreatestkillersintheWesternworldisheartdisease.Thedeathratefromthediseasehasbeenincreasingatanalarmingspeedforthepastthirtyyears.TodayinBritain,forexample,aboutfourhundredpeopleadaydieofheartdisease.Westernhealthcaresystemsarespendinghugesumsofmoneyonthesurgicaltreatmentofthedisease.Thisemphasisontreatmentisclearlyassociatedwiththetechnologicaladvancesthathavetakenplaceinthepasttentofifteenyears.Inthistime,moderntechnologyhasenableddoctorstodevelopnewsurgicaltechniquesandprocedures.ManyopeationsthatwereconsideredimpossibleafewyearsagoarenowperformedeverydayinU.S.hospitals.Theresulthasbeenarapidincreaseinheartsurgery.Althoughthereisnodoubtthatalargenumberofpeoplebenefitfromheartsurgery,criticsofourhealth-caresystemspointoutthattheemphasisonthesurgicaltreatmentofthediseasehasthreecleardisadvantages.First,itattractsinterestandfinancialresourcesawayfromthequestionofprevention.Second,itcausesthecostsofgeneralhospitalcaretorise.Afterhospitalsbuytheexpensiveequipmentthatisnecessaryformodernheartsurgery,theymusttrytorecoverthemoneytheyhavespent.Todothis,theyraisecostsforalltheirpatients,notjustthosepatientswhosetreatmentrequirestheequipment.Thethirddisadvantageisthatdoctorsareencouragedtoperformsurgery--evenonpatientsforwhomanoperationisnotatallnecessary--becausetheequipmentandsurgicalexpertiseisavailable.Afederalgovernmentofficerecentlysaidthatmajorheartsurgerywasoftenper-formedeventhoughitschancesofsuccesswerelow.Inonetypeofheartsurgery,forexample,only15percentofpatientsbenefitedfromthesurgery.Intherecentpast,medicalresearchershavebeguntoemphasizethefactthatheartdiseaseisassociatedwithstress,smokingandalackofexercise,andwecanoftenreducetheriskofheartdiseasebypayingmoreattentiontothesefactors.Moreandmorepeoplearerealizingthatthereisaconnectionbetweenheartdiseaseandthewaytheylive.Asaresultofthisnewawareness,attitudestowardhealtharechanging.Inthepast,peopletendedtothinkthatitwassufficientforgoodhealthtohaveagooddoctorwhocouldbereliedontoknowexactlywhattodowhentheybecameill.Nowtheyarerealizingthatmerelyreceivingthebesttreatmentforillnessorinjuryisnotenough.Theyarelearningthattheymusttakemoreresponsibilityfortheirownhealth.Todaymanypeoplearechangingtheirdietaryhabitsandeatingfoodwithlessfatandcholesterol.Manyarepayingmoreattentiontoreducingstressintheirlives.ThenumberofsmokersintheUnitedStatesisnowfarbelowtheleveloftwentyyearsagoasmanypeoplesucceedinbreakingthehabitandasfewerpeopletakeitup.Moreandmorepeopleareawareofthebenefitsofregularexerciselikewalking,running,orswimming;somehavebeguntowalkorridebicyclestoworkinsteadofdriving.MillionshavebecomemembersofhealthclubsandhavemadehealthclubsoneofthefastestgrowingbusinessesintheUnitedStatestoday.Andnowthebeneficialeffectsofthesechangingattitudesandbehaviorsarebeginningtoappear:anencouragingdecreaseindeathsfromheartdisease.16-B.DietingFourWaytoHealthAlmosteveryoneconsidersgoingonadietsometimeinhisorherlife.All,regardlessofsexandage,havesomethingincommon--losingweightandlosingitfast.Thoughtheircommonaimmayseembasicallygood,theyprobablydonotrealizethatmisguideddietingcandomoreharmthangoodtotheirhealth.Goingontoostrictadietcandestroythebalanceofchemicalsinthehumanbody.Thishappensbecausewhenthebodyissuddenlygivenmuchlessfoodthanusual,itfeelsasthoughitisbeingattackedandtrieshardtoprotectitselfbysavingenergy.Itdoesthisbyslowingdownmetabolism,theprocessbywhichthefoodweeatisconvertedintoenergy.Asenergyissuppliedtothebodyataslowerandslowerrate,dietersgraduallybecomesoweakthattheycandonothing.Theysoonloseinterestineverythinggoingonaboutthem,andtheirresistancetoillnessbecomessolowthattheyareeasilyattackedbyoneillnessafteranother.Mostofthosewhodietknowthatfoodslikerice,bread,potatoes,cakes,sweets,fruitsandsomevegetablescontaincarbohydrates,andsocanmakeonefat.Whattheydonotrealize,however,isthatcarbohydratesareourbodies’mainsourceofenergy,andthatthesefoodsalsocontaincomponentsessentialforthecompositionofsubstancesthatareneededtokeepthebodyhealthy.Asaresult,theytrytoavoideatingthesefoods,andconsequently,theybecomeweakerandlesshealthy.Theybegintohavedifficultysleepingproperlyandstarttosufferfromradicalmoodchanges.Inmoreseriouscases,theyevenbegintoshowsignsofmentalillness.1tisstrangeenoughthatmoststrictdietsrecommendartificialsweetenerstotaketheplaceofsugarandothernaturalsweeteners.Infact,suchartificialsweetenersactuallyincreaseone’sappetiteandleadtoone’seatingevenmorethanusual.Ofcourse,thefactthatmisguidedformsofdietingresultinsomanyproblemsdoesnotmeanthatnodietingissafeoralldietingisharmfultothehealth.Properdietingcannotonlyhelpapersonloseuglyexcessfat,butcanalsohelphimorhertokeepitoffandtoleadamoreactive,happierandhealthierlife.Youmightaskjustwhataproperdietis.Well,simplyexpressed,aproperhealthydietisonethatiswell-balanced,or,inotherwords,onethatincludesenoughbutnottoomanyofthekindsoffoodsthatprovidethebodywiththenutrientsthatitneedstofunctionproperly.Themostimportantofthesenutrientsarethemacronutrients:proteins,carbohydratesandfats.Thebodyneedsfairlylargeamountsofproteinsandcarbohydratesforbuildingmaterialandenergy.Meat,fish,eggs,milk,cream,andnutsallcontainproteinsandfoodslikerice,bread,potatoes,etc.containcarbohydrates.Thebodyneedsfattokeepitfromthecoldandtoprovideaprotectivelayerfortheorgans,butonlyinsmallquantities.Vitaminsandmineralssuchasiron,calcium,areanothergroupofessentialnutrients,thoughthebodydoesnotneedasgreataquantityoftheseasitdoesthemacronutrients-proteins,carbohydratesandfats.Therearetwotypesofvitamins,water-solublevitaminsandfat-solublevitamins.Water-solublevitaminslikevitaminCandtheB-groupvitaminsdonotstayinthebodylongandsofoodscontainingthesevitaminsneedtobetakenratheroften.Ontheotherhand,thefat-solublevitamins,vitaminsA,D,EandKstayinthebodyforlongperiodsoftimeandsothereisnoneedtotakefoodscontainingthemsooften.Onewayofgettingenoughnutrientswhilekeepingone’sweightdownistotakesubstitutesforfoodswhichcontaintoomuchfat.Forexample,insteadofregularmilk,onecantakeskimmedmilk,whichcontainsasmanyproteinsandmineralsasregularmilkbuthashadthefatremoved.Inthesameway,vegetableoilcanbeusedforcookinginsteadofanimaloil.17-A.PanicandItsEffectsOneafternoonwhileshewaspreparingdinnerinherkitchen,AnnePeters,a32-year-oldAmericanhousewife,suddenlyhadseverepainsinherchestaccompaniedbyshortnessofbreath.Frightenedbythethoughtthatshewashavingaheartattack,Annescreamedforhelp.HerhusbandimmediatelyrushedAnnetoanearbyhospitalwhereherpainswerediagnosedashavingbeencausedbypanic,andnotaheartattack.MoreandmoreAmericansnowadaysarehavingpanicattacksliketheoneexperiencedbyAnnePeters.BenjaminCrocker,apsychologistattheUniversityofSouthernCalifornia,revealthatasmanyastenmillionadultAmericanshavealreadyexperiencedorwillexperienceatleastonepanicattackintheirlifetime.Moreover,studiesconductedbytheNationalInstituteofMentalHealthintheUnitedStatesdisclosethatapproximately1.2millionadultindividualsarecurrentlysufferingfromsevereandrecurrentpanicattacks.Theseattacksmaylastforonlyafewminutes;some,however,continueforseveralhours.Thesymptomsofpanicattacksbearsuchremarkablesimilaritytothoseofheartattacksthatmanyvictimsbelievethattheyareindeedhavingaheartattack.Panicattackvictimsshowthefollowingsymptoms:theyoftenbecomeeasilyfrightenedorfeeluneasyinsituationswherepeoplenormallywouldnotbeafraid;theysuffershortnessofbreath,experiencechestpains,aquickheartbeat,suddenfitsoftrembling,afeelingthatpersonsandthingsaroundthemarenotreal;andmostofall,afearofdyingorgoingcrazy,Apersonseizedbyapanicattackmayshowallorasfewasfourofthesesymptoms.Therehasbeenalotofexplanationsastothecausesofpanicattacks.Manyclaimthatpsychologicalstresscouldbealogicalcause,butasyet,noevidencehasbeenfoundtosupportthistheory.However,studiesshowthatmorewomenthanmenexperiencepanicattacksandpeoplewhodrinkalotaswellasthosewhousedrugsaremorelikelytosufferattacks.Itisreportedthatthereareatleastthreesignsthatindicateaper-sonissufferingfromapanicattackratherthanaheartattack.Thefirstisage.Peoplebetweentheagesof20and30aremoreoftenvictimsofpanicattacks.Thesecondissex.Morewomensufferfromrecurrentpanicattacksthanmen.Thethirdisthemultiplicityofsymptoms.Apanicattackvictimusuallysuffersatleastfourofthepreviouslymentionedsymptoms,whileaheartattackvictimoftenexperiencesonlypainandshortnessofbreath.Itisgenerallyagreedthatapanicattackdoesnotdirectlyendangeraperson'slife.Allthesame,itcanunnecessarilydisruptaperson'slifebymakinghimorhersoafraidofhavingapanicattackinapublicplacethatheorshemayrefusetoleavehomeandmayeventuallybecomeisolatedfromtherestofsociety.Dr.Crocker’sadvicetoanypersonwhothinksheissufferingfromapanicattackistoconsultadoctorforamedicalexaminationtoruleoutthepossibilitiesofphysicalillnessfirst.Onceithasbeenconfirmedthatheorsheis,infact,sufferingfromapanicattack,thevictimshouldseekpsychologicalandmedicalhelp.17-B.Sleepwalking?FactorFancy?Thereisanendlesssupplyofstoriesaboutsleepwalkers.Personshavebeensaidtoclimbonroofs,solvemathematicalproblems,composemusic,walkthroughwindows,andcommitmurderintheirsleep.InRevere,Massachusetts,ahundredpolicemensearchedforalostboywholefthishomeinhissleepandwokeupfivehourslateronastrangesofainastrangelivingroom,withnoideahowhehadgotthere.AttheUniversityofIowa,astudentwasreportedtohavethehabitofgettingupinthemiddleofthenightandwalkingthree-quartersofamiletotheIowaRiver.Hewouldtakeaswimandthengobacktohisroomtobed.AnexpertonsleepinAmericaclaimsthathehasneverseenasleepwalker.Heissaidtoknowmoreaboutsleepthananyotherlivingman,andduringthelastthirty-fiveyearshaslostalotofsleepwatchingpeoplesleep.Sayshe,"ofcourse,IknowthattherearesleepwalkersbecauseIhavereadabouttheminthenewspapers.Butnoneofmysleeperseverwalked,andifIweretoadvertiseforsleepwalkersforanexperiment,IdoubtthatI’dgetmanytakers."Sleepwalking,nevertheless,isascientificreality.Itisoneofthosestrangephenomenathatsometimesborderonthefantastic.Whatiscertainaboutsleepwalkingisthatitisasymptomofemotionaldisturbance,andthattheonlywaytocureitistoremovetheworriesandanxietiesthatcauseit.Doctorssaythatsleepwalkingismuchmorecommonthanisgenerallysupposed.Manysleepwalkersdonotseekhelpandsoareneverputonrecord,whichmeansthatanaccuratecountcanneverbemade.Thequestionis:Isthesleepwalkeractuallyawakeorasleep?Scientistshavedecidedthatheisabouthalf-and-half.Dr.ZeldaTeplitz,whomadeaten-yearstudyofthesubject,says,"Thesleepwalkerisawakeinthemusculararea,partiallyasleepinthesensoryarea.”Inotherwords,apersoncanwalkinhissleep,movearound,anddootherthings,buthedoesnotthinkaboutwhatheisdoing.Whatarethechancesofasleepwalkercommittingamurderordoingsomethingelseextraordinaryinhissleep?Dr.Teplitzsays,"Mostpeoplehavesuchgreatinhibitionsagainstmurderorviolencethattheywouldawakenifsomeonedidn'twakethemup."Ingeneral,authoritiesonsleepwalkingagreewithher.Theythinkthatpeoplewillnotdoanythingintheirsleepthatisagainsttheirownmoralstandard.Asforthepublicizedcases,Dr.Teplitzpointsout,"Sleepwalkingitselfisdramatic...sleepwalkerscanalwaysfindanaudience.Ithinkthatsomeoftheirtalltalesgetexaggeratedinthetelling.”Inherownrecordsofcasehistories,thereisnotonesleepwalkerwhoevergotbeyondhisownfrontdoor.Toprotectthemselves,somesleepwalkershavebeenknowntotiethemselvesinbed,locktheirdoors,hidethekeys,boltthewindow,andtakeallsortsofmeasurestowakethemselvesiftheyshouldgetoutofbed.Curiouslyenough,theyhaveanunusualwayofavoidingtheirowntrapswhentheysleepwalk,sononeoftheirtricksseemtoworkverywell.Somesleepwalkerstalkintheirsleeploudlyenoughtowakesomeoneelseinthefamilywhocanthenshakethembacktotheirsenses.Childrenwhowalkintheirsleepusuallyoutgrowthehabit.Inmanyadults,too,theconditionismoreorlesstemporary.Ifithappensoften,however,thesleepwalkershouldseekhelp.Althoughsleepwalkingitselfisnothingtobecomealarmedabout,theproblemsthatcausethesleepwalkingmaybeveryserious.18-A.WhyAreMapsDrawnwithNorthattheTop?Nowitishardtovisualizeamapthatdoesnotfeaturenorthatthetop,butthiswasnotalwaysso.Theoldestknownmapintheacceptedsenseofthewordwasdrawnabout3,800BC,andrepresentstheriverEuphratesflowingthroughnorthernMesopotamia,Iraq.This,andothersthatfollowedit,werelittlemorethanroughsketchesoflocalizedfeatures;itwasnotuntilmanycenturieslaterthattheancientGreeksplacedthescienceofmap-makingonasoundfooting.AttheforefrontofthepioneersinthefieldwastheGreekmathematicianandphilosopherClaudiusPtolemaeus(c.AD90?168),morepopularlyknowntohistoryasPtolemy.Thelastgreatscientistoftheclassicalperiod,hewasthefirsttodrawamapthatwasbasedonallavailableknowledge,ratherthanguessorimagination.Earlier,theBahylonianshadattemptedtomaptheworld,buttheypresenteditintheformofaflatteneddiscratherthanasphere,whichwastheformadoptedbyPtolemy.Giventhestateofknowledgeofthosetimes,hegotthingswrong;forexample,hisestimateofChinaandtheAtlanticOceanwasfarfrombeingaccurate.Nevertheless,itwasausefuleffort,andthemapremainedaworkofreferenceforoverathousandyears.Infact,ChristopherColumbususedaversionofitwhenhesetsailinsearchoftheNewWorld-whichcausedhimsomenavigationalproblems,sincePtolemyhadcalculatedwronglythesizeoftheAtlanticandwasunawarethatthePacificOceanexisted.ThereallyimportantthingaboutPtolemy'smapwasthatnorthwasatthetop.ThereasonforthiswasthathedecidedtoorientatethemapinthedirectionoftheVoleStarsincePolariswastheimmovableguidinglightinwhichthevoyagersofthateraplacedtheirtrust.NorthatthetopremainedtheacceptedarrangementuntiltheearlyMiddleAges,whentheChurchbegantointerfereseriouslywiththeadvanceofscience.InaccordancewiththeordersoftheChurch,mapswerestillproducedinaccordancewithPtolemy'sprinciples?butnowJerusalemwasthecentralfeature,asitwasheldtobethecenteroftheChristianfaith,andeastwasmovedtothetop.Thesemapsareoftencalled"T"Mapsbecausetheyshowonlythreecontinents-Europe,AsiaandAfrica-separatedbythe"T"formedbytheMediterraneanSeaandtheRiverNile.Fromanavigationalpointofview,theywerealmostuseless.Moreaccuratemapsbegantoappearinthe14thcentury,withthespreadoftradeandincreasingrelianceonthecompass.Onceagain,northassumeditsrightfulplaceatthetopofmaps.18-B.YouHaveaChoiceTwotrainsaretravelingsidebysideandatthesamespeedalongparalleltracks.Weareseatedinoneofthetrains,andwithuswehaveaspecialspeedometerthatmeasurestheirrelativespeech.Sincethetrainsaretravelingatthesamespeed,theirrelativespeediszero;thespeedometerthereforereads"0."Suddenlytheothertrainseemstostartpullingaheadofours.Thespeedometershowsareadingof10milesperhour.Theothertrainhasapparentlyincreaseditsspeed.Hutcanweheabsolutelycertainofthisincrease?Ifyouranswerisyes,youarewrong.Youarewrongbecauseallthatweknowisthattherelativespeedbetweenthetwotrainschangedfrom0mphto10mph.Nothingmore.Thischangecouldhavebeenbroughtaboutinoneoftwoways:1.Theothertrainincreaseditsspeed.2.Ourtraindecreaseditsspeed.Therearethustwopossibleexplanationstoaccountforthechangeinspeed,butwedon'tknowwhichoneisright.Furthermore,regardlessofwhichexplanationwechoose,theendresultwillhethesame:theothertrainwillarriveatthestationfirst.Soitmakesnodifferencewhetherwesaythattheothertrainincreaseditsspeedorthatourtraindecreaseditsspeed.Sincebothexplanationsleadtothesameresult,youcanchooseeitherone.Whenevertwothingsarerelative,youcanchooseeitheroneofthem.Theconverseisalsotrue:wheneveryouhaveachoicebetweentwothingsthatareequallypossible,thenthethingsarerelative.Thereisnoreason,exceptconvenience,forchoosingoneexplanationovertheother.Therelativespeedbetweenthetrainsremainsthesame,10mph;andtheendresultwillbethesame.Nowlet抯supposethatbothtrainsareattherailroadstationloadingandunloadingpassengersandbaggage.Ahalf-hourpasses.Aswelookattheothertrainthroughourwindow,weseethatourtrainseemstostartmoving,smoothlyandslowly.Foraminuteorso,ourtrainseemstotravelatauniformspeed.Ourspecialspeedometershowsthattherelativespeedbetweenthetwotrainsis20mph.Butaswelookoutourwindow,wesuddenlyseethelastcoachoftheothertraindisappearfromsightandnoticethemotionlessstationbehindit.Sowearenotmovingafterall.Theothertrainhasbeenmoving!Thispeculiarandoftenfrustratingexperienceisaneffectofrelativemotion.Atthetrainstationwecannottellwhetheritwasourtrainthatchangeditsspeedfrom0mphto20mphorwhetheritwastheothertrainthatchangeditsspeedfrom0mphto20mph.Onlyaftertheothertrainpulledoutofthestationcouldweseethatit,andnotourtrain,wasmoving.Nowletusagainraisethequestionthatwasraisedatthebeginningofthisarticle:canwebeabsolutelycertainthattheothertraindidindeedincreaseitsspeed,andinthiscasepulloutofthestation?Ifyouranswerisyes,thenyouarewrongagain.Allwecanbecertainofisthattherelativespeedbetweenthetwotrainschanged.Theseexamplesillustrateanimportantprincipleinthespecialtheoryofrelativity.IfAappearstobemovingatasteadyspeedrelativetoB,wecannotknowforsureifitisAthatisreallymoving.PerhapsAisstandingstill,andBismoving.Orperhapsbotharemoving.Accordingtorelativity,thereisnoexperimentthatcanbedevisedtosolvetheproblem.Asthereisnowayofdecidingwhichofthetwoobjectsismoving,wecanchooseeitheroneasthemovingobject.Thereasonisthattheirmotionisrelative,andrelativity,aswehaveseen,meansthatwehaveachoice.Thisprinciple-thatiftwoobjectsareinuniformmotionrelativetoeachother,itisimpossibletodecidewhichoneismovingandwhichoneisatrest-appliestoallobjectsmovinguniformlyinastraightlinethroughtheuniverse.Inrelativityyou’llfindthatwheneveryouhaveachoiceamongthingsthatareequallypossible,youaredealingwithrelativethings.Forexample,time,whichismeasuredwithclocksandwatches,isrelativebecauseitcanbeshownthatthereismorethanonesystemoftime.Allsystemsoftimeareequallypossibleandyoucanchooseanysystemyouwish.19-A.AnimalsatRisk:WhoCares?Ananimalspeciesbecomesextinctwhenitfailstoproduceenoughyoungineachgenerationtokeeppacewiththedeath-rate.Wecantellfromfossilevidenceinrocksthatmanylivingspecieshavebecomeextinctoverthemillionsofyearssincelifebegan.Itisanaturalprocessandextinctionisthefateofanyanimalthathasspecializedtoofartochangewhenitsenvironmentchanges,orhastocompetewithabetter-adaptedandmorepowerfulanimal.Becauseofremarkabletechnicaldevelopmentsduringthepastfewcenturies,manhasdestroyedornearlydestroyedsomespeciesbykillingthematsucharatethattheycouldn'tproduceenoughoffspring,orbycompletelychangingtheirnaturalenvironmentatsurprisingspeed.Anumberofexamplescanbegivenofthewayinwhichnaturalenvironmentsarebeingrapidlychanged-Amazonia,forinstance.Thereiseverylikelihoodthatmanyspeciesofanimalswillbemadeextinctbecauseoftheseandsimilarclearancesofnaturalvegetation.Largenumbersofanimalshavebeenhuntedandkilledforfood.TheNorthAmericanbuffaloisacaseofthenear-extinctionofaspeciesthroughhunting.Oftenthenumbersaresogreatthehuntersmaynotrealizethedanger.Butevenwhenthedangeriswidelypublicized,thefinancialrewardsforthehuntersmaybesogreatthattheychoosetoignorethethreattothespecies.Attitudeslikethishaveledtohunterskillinganimalsforfurs,forivoryormerelyforornaments.Aslightvariationonthisiswhentouristshuntanimalsfortrophies.Magnificentcreaturessuchaslionsandtigershavebeenhuntedoutofexistenceinsomepartsoftheworld.Itisimportanttorealise,though,thatanimalsaresometimeskilledoutoffear.Bigcatsarekilledinthisway.Andanimalsaresometimeskilledoutofawishtoreducenumberstohelpthespeciestosurvive.ThekillingoftheCanadiansealsisclaimedtobeforthispurpose,andtheuseoftheirskinsforfursisonlyaby-product.Manypeopleareconcernedaboutanimalsandwildlifeconservation.Onewaytopreservespeciesunderthreatofextinction-whateverthecause-istoremovethemtozoosandparksandbreedthemthere.Thereisalwaysthechancethatenoughoffspringwillbeborntoreturnthemonedaytotheirnaturalenvironment-provideditstillexists,andthathuntersdon'tkillthemagain!Anothermethodistoprotecttheanimalsintheirnaturalenvironmentbycreatingwildlifereservesandparksandusinggamewardenstolookafterthem.Buttheparksarelarge,thewardensfewandthedeterminationofhuntersverygreat.Earlyin1980wardensandhuntersclashedinEastAfrica.Thehunterswerearmedwithmodernweaponsandseveralpeoplewerekilled.Thereisgreatpleasureinwatchingwildlifeinnaturalornear-naturalenvironments,andtourismcanaddtotheincomeofcountries.Theanimalsarestillresources-butinaverydifferentform.19-B.TheKillerSmogsOnthenightofDecember1,1930,adensefogmovedovertheMeuseVal