大学英语四级考试15选10专项训练

PAGE5-大学英语四级考试15选10专项训练UnitOneDirections:Inthispassagetherearetenblanks.Youarerequiredtoselectonewordforeachblankfromalistofchoicesgiveninawordbankfollowingthepassage.Readthepassagethroughcarefullybeforemakingyourchoices.Eachchoiceinthebankisidentifiedbyaletter.PleasemarkthecorrespondingletterforeachitemonAnswerSheet2withasinglelinethroughthecentre.Youmaynotuseanyofthewordsinthebankmorethanonce.Questions1to10arebasedonthefollowingpassage.Lookingbackonyearsoflivinginaworking-classhomeintheNorthofEngland,Ishouldsaythatagoodlivingroommust11threeprincipalthings:homeliness,warmthandplentyofgoodfood.Theliving-roomisthewarmheartofthefamilyand12oftenslightlystuffytoamiddle-classvisitor.Itisnotasocialcentrebutafamilycenter;littleentertaininggoesonthereorinthefrontroom,ifthere13tobeone;youdonotentertaininanythingapproachingthemiddle-class14Thewife'ssociallifeoutsideher15familyisfoundoverthewashing-line,atthelittleshoponthecorner,visitingrelativesatamoderate16occasionally,andperhapsnowandagainavisitwithherhusbandtohispuborclub.Apartfromthesetwoplaces,hehasjusthisworkandhisfootballmatches.Theywillhave,eachofthem,friendsatalltheseplaces,whomaywellnotknowwhattheinsideoftheirhouseislike,havingnever"steppedacrossthethreshold,"astheold17phrasehasit.Thefamilyhearthis18forthefamilyitself,andthosewhoare"somethingtous"(anotherfavoriteformula)andwholookinforatalkorjusttosit.Muchofthefreetimeofamanandhiswifewill19bepassedatthathearth.Juststayinginisstilloneofthemostcommonleisure-time20A.happensB.professionsC.senseD.neverthelessE.fashionedF.distanceG.immediateH.usuallyI.occupationsJ.preservedK.imitateL.provideM.thereforeNreserved0.contributeUnitTwoPassage2Flyingoveradesertareainanairplane,twoscientistslookeddownwithtrainedeyesattreesandbushes.Afteranhour's11oneofthescientistswroteinhisbook,"Lookherefor12metal."Scientistsinanotherairplane,flyingoveramountainregion,senta13tootherscientistsontheground,"Goldpossible."Walkingacrosshillyground,fourscientistsreported,"Thisgroundshouldbesearchedformetals."Fromanairplaneoverahillywastelandascientistsentbackbyradiooneword,"Uranium."NoneofthescientistshadX-rayeyes:theyhadno14powersforlookingdownbelowtheearth'ssurface.Theywere15puttingtouseoneofthenewestmethodsof16mineralsintheground—usingtreesandplantsas17thatcertainmineralsmayliebeneaththegroundonwhichthetreesandplantsaregrowing.Thisnewestmethodofsearchingformineralsis18onthefactthatmineralsdeepintheearthmay19thekindofbushesandtreesthatgrowonthesurface.AtWatsonBarCreek,abrooksixthousandfeethighinthemountainsofBritishColumbia,Canada,amineralsearchgroupgatheredbagsoftreeseeds.Boxeswerefilledwithsmallbranchesfromthetrees.Rootsweredugandputintoboxes.Eachbagandboxwas20marked.Inascientificlaboratorythepartsoftheforesttreeswereburnedtoashesandtested.Eachsmallpartwasexaminedtolearnwhetherthereweremineralsinit.A.signsB.sufficientlyC.locatingD.affectE.merelyF.magicG.hintsH.carefullyI.findingJ.messageK.flightL.probableM.revealingN.basedO.informationUnitThreePassage2America'smostfamouswomanistheGoddessofLiberty,i.e.theStatueofLiberty.Itwasfirstthoughtofin1865byEdouarddeLaboulayeanddesignedbyanotherFrenchman,FredericBartoldi.Theywantedto11libertyandfriendship.Itwashopedthatthemonumentwouldbecompletedby1876whenAmerica12itscentennial.Fundraisingandthe13ofthestatueinFrancewentslowly.Itwas1885whenthe214cratescontainingthestatuereachedNewYork.Americanswereinitially14fortheyhadnotraisedthemoneytopayfortheerectionofthebase.Fundraisingbypopularsubscriptionwasbehind15.OnefundraisingmethodusedwastohavepopularAmericanswriteletterswhichwerethensoldinpublic.Thebaseandstatue,16272feettall,werecompletedin1886.Froma17standpoint,thestatueisamarvel.TheinnerstructurewasdesignedbytheFrenchengineer,AlexandreEiffel.Hisdesignforthestressedcopperskinofthestatueanticipatedmanyofthe18utilizedinmodernaircraft.Afteracentury,themonumentbegantoshowsignsofgettingworsein19.JustasFrenchmenhadcreatedtheStatue,soitwaswithrestoration.AFrenchmannotedthedecayandFrenchandAmericancraftsmenandcontributionsbroughtabouttherenewaloftheStatueintimeforitscentennial.Libertyisstill20inFranceandtheUnitedStatesA.completelyB.measuresC.popularD.togetherE.honorF.manufactureG.scheduleH.rewardI.celebratedJ.principlesK.embarrassedL.technicalM.voluntaryNconditions0.discouragedUnitFourPassage2SophyBrentcametovisitmenearlyeveryday.Shemademefeeluneasymostofthetime.Shesmoked11andneverusedanashtray.ShefollowedmeintothekitchenwhileImadeteaorcoffeeorsupperand12herselftothechildren'sorangejuice.Shemadeagreathitwithmytwo-year-olddaughterFlora,whowould13aboutherforhoursandrefertoherlovinglyas"sofa",andshewasalwaystalkingaboutmyhusbandandaskingmewherehewas.Icouldnotdecidewhyshechosemy14,althoughIrealizedthatnobodyelsepaidherverymuchattention.Hersituationwasverydifficultinthatshewas15outofdramaschoolandonlynineteen,butbeing16toplayaleadingpartinacompanyoffairly17andexperiencedactors.Theywouldnothavelikedhermuchevenifshehadbeengood,andas,fromallaccounts,shewasnotgoodsotheytookevery18torunherdown.IthinkshethoughtthatIwastheonlypersonaroundwhowasbothunconnectedwiththetheatreandtolerably19.Toassociatewithmewasnot,atanyrate,tostepdownthescale.Andformypart,althoughIfelttroubledbyherIdidnotdislikeher.Therewassomethinggenuinelyoutstandinginherpersonality,andshehadsuchphysical20thatwithmeshecouldgetawaywithanything.Shewasnicetohavearound,likeflowersorabowloffruit.A.helpedB.smartB.constantlyD.treatedE.requiredF.supremeG.hangH.charmI.continuallyJ.companyK.opportunityL.distinguishedM.straightN.partnerO.disappointedUnitFivePassage2Manypeopleoftenenjoyeatingouteitherbeforeorafteravisittothetheatre.However,mostofuswouldratherkeepthetwo11separate.Onemanwhothinksthattheycanbesuccessfullycombinedhasnotonlyexpressedhisideasinarecentbook,butalsosetupanestablishmentwherethetheoryisputvery12intopractice.ThemanisPaulThornton,andtheplaceistheHollics,anoldfarmhouse.WheneverIvisitanewrestaurant,Ifeelthesameexcitementthatkeentheatre-goersmustexperienceonopeningnight.IhadthisfeelinglastFridayeveningatdusk,asmywifeandIweretakingawalkinthebeautifulgardensoftherestaurant13afterwehadarrived.Dinnerwasasexcellentaswehadbeen14.Thereisnomenu,forMr.Thorntoncreateshismealsratherasadirectorproducesaplay.Nevertheless,thevariouscombinationsof15ateachcoursearealways16asiftheyweredonebymagic.Heandhisteamofhighlyskilledhelpersserve,cutandcookthefood,movingaboutthe"stage"asconfidentlyas17actors.Themealisasdifferentfromwhatonefindsinordinaryrestaurantsasa18performanceofAMobviouslyNwithstandOharshUnitThirteenPassage2Whatisyourfavoritecolor?Doyoulikeyellow,orange,red?Ifyoudo,youmustbeanoptimist,aleader,anactivepersonwho11life,peopleandexcitement.Doyouprefergreysandblues?Thenyouareprobablyquiet,shy,andyouwouldratherfollowthanlead.You12tobeapessimist.Atleast,thisiswhatpsychologiststellus,andtheyshouldknow,becausetheyhavebeenseriouslystudyingthemeaningofcolorpreference,aswellastheeffectthatcolorshaveonhumanbeings.Theytellus,amongother13,thatwedonotchooseourfavoritecoloraswegrowup—wearebornwithourpreference.Ifyouhappentolovebrown,youdidso,assoonasyouopenedyoureyes,oratleastassoonasyoucouldseeclearly.Colorsdo14ourmoods—thereisnodoubtaboutit.Ayellowroommakesmostpeoplefeelmorecheerfulandmorerelaxedthanadarkgreenone;andareddressbringswarmthandcheertothesaddestwinterday.Ontheotherhand,blackis15.AblackbridgeovertheThamesRiver,nearLondon,usedtobethe16ofmoresuicidesthananyotherbridgeinthearea—untilitwasrepaintedgreen.Thenumberofsuicideattemptsimmediatelyfell17;perhapsitwouldhavefallenevenmoreifthebridgehadbeendoneinpinkorbabyblue.Lightand18colorsmakepeoplenotonlyhappierbutmoreactive.Itisan19factthatfactoryworkersworkbetter,harder,andhavefewer20whentheirmachinesarepaintedorangeratherthanblackorgrey.A.brightB.sceneC.whollyD.favorE.factsF.depressingG.accidentsH.interfereI.establishedJ.incidentsK.disgustingL.sharplyM.enjoysN.tendO.influenceUnitFourteenPassage2Womenarealsounderrepresentedintheadministrationandthisisbecausetherearesofewwomen11professors.In1985,RegentBerylMilburnproducedareportblastingtheUniversityofOneofthepositiveresultsfromherstudywasasystem-wideprogramtoinformwomenofavailableadministrativejobs.CollegeofCommunicationAssociateDean,PatriciaWitherspoon,saiditisimportantthatwomanbe15whenitcomestorelocatingiftheywanttoAlthoughawomanmayfaceachilly17oncampus,manytimesinorderforhertosucceed,shemustriseabovetheproblemsaroundherandconcentrateonherwork.Untilwomenmakeupagreater18oftheseniorpositionsintheUniversityandallacademia,inequalitieswillexist."WomenneedtospendtheirenergiesandtimedoingscholarlyactivitiesthatareimportanthereattheUniversity."Spirdusosaid."Iftheydothattheywillbe19inthissystem.Iftheyspendtheirtimeinlittlegroupsmourningthesexualdiscriminationthattheythinkexistshere,theyare20wastingvaluablestudytime."A.fullB.recalledC.improvementD.riseE.encouragingF.flexibleG.recognizedH.idlyI.ratioJ.persuadingK.movableL.possiblyM.successfulN.climateO.percentageUnitFifteenPassage2InOctober1987,theNationalBoardforProfessionalTeachingStandardsbeganitsworktosetnewstandardsofaccomplishmentfortheteachingprofessionandtoimprovethe11ofeducationavailabletoallchildrenintheUnitedStates.Teachersare12tostudentsandtheirlearning.Theymustactonthebeliefthatallstudentscanlearn.Theymustrecognize13differencesintheirstudentsandadjusttheirpractice14.Theymustknowthattheirmissionextendsbeyonddevelopingthecognitivecapacityoftheirstudents.Theymustbe15withtheirstudents'self-concept,withtheirmotivation,andwiththedevelopmentofcharacter.Teachersmustknowthesubjectstheyteachandhowtoteachthem.Theymust16specializedknowledgeofhowtoconveyasubjecttostudents.Teachersareresponsibleformanagingandmonitoringstudentlearning.Theymustcallon17methodstomeettheirgoals,knowingandbeingableto18avarietyofinstructionalskills.Teachersmustthinksystematicallyabouttheirpracticeandlearnfromexperience,seekingthe19ofothersanddrawingoneducationresearchandscholarshiptoimprovetheirpractice.Asmembersoflearningcommunities,teacherscontributetoschooleffectivenessbycollaboratingwithotherprofessionals.Theytake___20ofcommunityresources,cultivatingknowledgeoftheirschool'scommunityasapowerfulresourceforlearning.A.employB.adviceC.quantityD.committedE.commandF.consultedG.manualH.approximatelyI.concernedJ.advantageK.multipleL.accordinglyM.individualN.embraceO.qualityUnitSixteenPassage2Ifyouarelookingforinformation,libraryshelvesareagoodplacetostart.Butifyouneedup-to-the-minutedataorhavespecializedneeds,youmayfindacomputerizeddatabasemoreuseful,lessexpensive,andlesstime11.Adatabase,afileofinformationononesubjectorfamilyofsubjects,canbestoredand12inacomputer'smemory.Thespeedofthecomputerthen13youtorecallanyiteminthisfilealmost14Thethreemaintypesofdatabasesarestatistical,bibliographic,andfulltext.Statisticaldatabasesstore15amountsofnumericaldata,suchaswageandpriceindexes,censusinformation,foreign16ratesandbondprices.Bibliographicdatabasesstorereferencestoandsummariesofarticlesinperiodicalsandnewspapers.Full-textdatabasesofferthecomplextextsofsuch17asnewspaper,magazine,andjournalarticles.Thousandsofdatabasesexisttoday,andtheirnumbersaregrowing.Manycompanieshavetheirin-housedatabase,whichis18toemployeesthroughcomputerterminalsormicrocomputers.Inaddition,severalhundredcommercialdatabasesarenowavailabletothe19,withliterallymillionsofitemsofinformationreadilyobtainable.Thesedatabases20specificfields,suchaslawandfinancialforecasting,orgeneralinformation,suchassportsandweatherdata.A.exchangeB.publicC.instantlyD.coverE.enablesF.consumingG.remainedH.materialsI.hideJ.intensivelyK.vastL.communicationsM.exhaustingN.accessible0.maintainedUnitSeventeenPassage2Nooneknowsexactlyhowmanydisabledpeoplethereareintheworld,but11suggestthefigureisover450million.ThenumberofdisabledpeopleinIndia12isprobablymorethandoublethetotalpopulationofCanada.IntheUnitedKingdom,aboutoneintenpeoplehavesomedisability.Disabilityisnotjustsomethingthathappenstootherpeople:aswegetolder,manyofuswillbecomeless13,hardofhearingorhavefailingeyesight.Disablementcantakemanyformsandoccuratanytimeoflife.Somepeoplearebornwithdisabilities.Manyothersbecomedisabledastheygetolder.Therearemany14disablingdiseases.Thelongertimegoeson,theworsetheybecome.Somepeoplearedisabledinaccidents.Manyothersmayhaveaperiodofdisabilityintheformofamentalillness.Allareaffectedbypeople'sattitudetowardsthem.Disabledpeoplefacemany15barriers.Nexttimeyougoshoppingortoworkortovisitfriends,imaginehowyouwould16ifyoucouldnotgetupsteps,orontobusesandtrains.Howwouldyoucopeifyoucouldnotseewhereyouweregoingorcouldnothearthetraffic?Butthereareotherbarriers;17canbeevenhardertobreakdownandignorance18representsbyfarthegreatestbarrierofall.Itisalmostimpossiblefortheable-bodiedtofullyappreciatewhattheseverelydisabledgothrough,soitisimportantto19attentiontothesebarriersandshowthatitistheindividualpersonandtheirability,nottheirdisability,which20A.inevitablyB.evaluationsC.estimatesD.manageE.aloneF.countsG.prejudiceH.physicalI.mobileJ.indifferentlyK.withdrawL.progressiveM.regularN.accountsO.drawUnitEighteenPassage2Socialcustomsandwaysofbehavingchange.Thingswhichwereconsideredimpolitemanyyearsagoarenow11.Justafewyearsago,itwas12impolitebehaviorforamantosmokeonthestreet.Nomanwhothoughtofhimselfasbeingagentlemanwouldmakea13ofhimselfbysmokingwhenaladywasinaroom.Customsalsodifferfromcountrytocountry.Doesamanwalkontheleftortherightofawomaninyourcountry?Ordoesn'tit14?Whatabouttablemanners?Shouldyouusebothhandswhenyouareeating?Shouldyouleaveoneinyourlap,oronthetable?TheAmericansandtheBritishnotonlyspeakthesamelanguagebutalso15alargenumberofsocialcustoms.Forexample,inbothAmericaandEnglandpeopleshakehandswhentheymeeteachotherforthefirsttime.Also,mostEnglishmenwillopenadoorforawomanoroffertheirseattoawoman,andsowillmostAmericans.16isimportantbothinEnglandandinAmerica.Thatis,ifadinnerinvitationisfor7o'clock,thedinnerguesteitherarrives17tothattimeorcallsuptoexplainhis18Theimportantthingtorememberaboutsocialcustomsisnottodoanythingthatmightmakeotherpeoplefeeluncomfortable—19iftheyareyourguests.Thereisanoldstoryaboutamanwhogaveaformaldinnerparty.Whenthefoodwasserved,oneoftheguestsstartedtoeathispeaswithaknife.Theotherguestswereamusedorshocked,butthe20calmlypickeduphisknifeandbeganeatinginthesameway.A.especiallyB.attainableC.closeD.delayE.consideredF.hostG.deliveryH.PreparationI.shareJ.foolK.specificallyL.acceptableM.matterN.Promptness0.careUnitNineteenPassage2TheeconomyoftheUnitedStatesafter1952wastheeconomyofawell-fed,almostfullyemployedpeople.Despite11alarms,thecountryescapedanypostwardepressionandlivedina12ofboom.Aneconomicsurveyoftheyear1955,atypicalyearofthe1950's,maybetypicalas13therapideconomicgrowthofthedecade.Thenationaloutputwas14at10percentabovethatof1954(1955outputwasestimatedat392billiondollars).Theproductionofmanufactureswasabout40percentmorethanithad15intheyearsimmediatelyfollowingWorldWarI.Thecountry'sbusinessspentabout30billiondollarsfornewfactoriesandmachinery.Nationalincome16forspendingwasalmostathirdgreaterthanithadbeenin1950.Consumersspentabout256billiondollars;thatisabout700milliondollarsaday,orabouttwenty-fivemilliondollarseveryhour,allroundthe17.Sixty-fivemillionpeopleheldjobsandonlyalittlemorethantwomillionwantedjobsbutcouldnotfindthem.Onlyagriculture18thatitwasnotsharingintheboom.Tosomeobserversthiswasasadreflectionofthemid-1920's.Asfarmers'shareoftheirproducts19,marketingcostsrose.Buttherewere,amongtheobserversofthenationaleconomy,afewwhowerenotasconfidentasthemajority.Thosefewseemedtofearthattheboomcouldnotlastlongandwould20leadtotheopposite—depression.A.eventuallyB.averagedC.graduallyD.stateE.valuedF.formG.declinedH.occasionalI.casualJ.arguedK.descendedL.complainedM.clockN.availableO.illustratingUnitTwentyPassage2Growthoftradewilldependgreatlyonavailabilityofenergysources.TheremaystillbeatrillionbarrelsofrecoverableoilintheMiddleEast.Buttheoilcrisisof1974has11torenewedinterestincoalandtoasearchfor12sourcesofenergy.Solar,geothermal,andnuclearenergywillplayalargeroleintheyearstocome.Solarenergyisavailablein13forms.Buildingscanbeheatedandcooledbydirectuseofsolarradiation,cropsandtrees,whicharethemostefficientconvertersofsunlightintoenergy,canbegrownfortheirenergypotential,wastescanbeburnedas14,sunlightcanbeconvertedintoDC(directcurrent)electricity,electricpowercanbe15fromthesun-warmedsurfacewatersoftheocean,andlastly,solarradiationcanbeconvertedintoheatthatwilldriveelectricpowergenerators.Seriousproblemsstillremainasto16andstorageofsolarenergy.Geothermalenergyistheenergycontainedwithintheearth.Heatisabundantlyavailabledeepintheearth'scoreandisconstantlybeingproduced.However,thisheatisusuallylocatedattoodeepalevelfor17exploitation.Inshort,verylittleisknownontheuseofgeothermalenergy,andithas18beenexploited.Nuclearenergyisproducedinnuclearpowerplants.Attheseplantsatomsofuraniumaresplit,thus19massesofenergy.Anothersourceofenergyunderdevelopmentisthenuclearfusionofcertainatomsofhydrogen.Thiscouldeventually20naturalgasasasourceofenergy.A.rarelyB.transformationC.fuelD.replaceE.ledF.alternativeG.commercialH.brieflyI.derivedJ.variousK.relievingL.releasingM.transportationN.financialO.describedUNIT21Likemostparents,geologistBrainAtwaterworriesabouthisdaughter'ssafety.Butthesedays,hehasanunusualconcern;Thepublicschoolshe11inSeattlehasunreinforcedbrickwalls,a12beingeasytocollapseduringearthquakes.Thesame13ofwallscrushedhundredsofthousandsofpeopleduringthe1976TangshanquakeinChina.Adecadeago,Atwaterwouldhavepaidlittlenoticetoschoolroomwalls.Butoverthelastseveralyears,heandotherscientistshavefound14signsthatthePacificNorthwesthasexperiencedgiantquakesinthedistantpastandthattheareamaybeheadedforadestructiveshockinthenearfuture.AtameetingoftheAmericanGeophysicalUnioninDecember,researchersdiscussedthe15uncoveredevidenceofquakepotentialinthePacificNorthwest.Whilesomeremainunconvincedthathugeearthquakes—withmagnitudesof8orhigher—doindeed16thisregion,agrowingnumberconsidersuchshocksaseriouspossibility.What'sworrisome,theysay,isthatnorthwesterncitiessuchasPortland,SeattleandVancouverhavenotpreparedforearthquakesofthismagnitude,whichcouldshaketheregion's17centerswithenoughforcetomaketherecentSanFranciscoareadamageseem18incomparison."Ithinkit'squitetruetosaythatnothinghasreallybeendesignedwithoneoftheseearthquakesinmind,"saysseismologistPaulSomervilleofWoodward.Atthemeeting,Somervilleandhiscolleagues19estimatesofthedegreeofshaking.PortlandandSeattlewouldsufferduringsucha20earthquake.A.massiveB.recentlyC.constructionD.displayedE.relativelyF.attendsG.typeH.strikeI.structureJ.participatesK.excessiveL.mildM.disturbingN.population0.presentedUnitTwenty-TwoPassage2Duringthenineteenthandtwentiethcenturies,migrationshavetakenplacewithin11countries;thecitieswiththeirindustrieshaveattractedpeopleawayfromthecountry.Thepossibilityofearningafixed12inafactoryorofficewasmoreattractivethanthepossibilityofstayingonthefarmandhavingone'swork13byfrost,storms,ordroughts.Furthermore,thedevelopmentofagriculturalmachinerymadeitpossibleforfewerpeopletodothesame14ofwork.Thus,atthesametimewhentheindustrialrevolutionmadeitpossibletoproducegoodsmore15andmorequicklyinfactories,agriculturalrevolutionalsotookplace.Insteadofleavingfieldsemptyeverythirdyear,farmersbegantoplantcloverorsomeothercropthatwould16thesoil.Insteadofusingonlyanimalfertilizer,farmersbegantousechemicalfertilizerstokeepthesoil•150•rich.ThesemethodshaveenabledFrenchfarmers,forexample,togetfivetimesasmuchwheataswas17fromthesamelandtwocenturiesago.Inmanycountriesfarmersfinditmore18toraiseonlyonecroporonekindofanimal.Theychoosethekindthatgivesthebestresults.Thentheysellallthattheyproduce,insteadoftryingtogrowalittleofeverythingandconsumewhattheygrow.Thisisamorefeasibletypeof19becausemodernmethodsandmachineryareadaptedtospecificanimalsandspecificcrops.Therefore,itwouldbetooexpensivetodoalltheworkbyhand,ortobuythe20neededforseveraldifferentkindsoffarming.A.salaryE.desertedI.equivalentM.destroyedB.freelyF.operationJ.enrichN.certainC.profitableG.amountK.fruitfulO.cheaplyD.obtainedH.paymentL.equipmentUnitTwenty-ThreePassage2ThedifferencebetweenaliquidandagasisobviousundertheconditionsoftemperatureandpressurecommonlyfoundatthesurfaceoftheEarth.Aliquidcanbekeptinanopencontainerandfillittothelevelofafreesurface.Agasformsnofreesurfacebuttendstodiffusethroughoutthe11available;itmustthereforebekeptinaclosedcontainerorheldbyagravitationalfield,asinthe12ofaplanet'satmosphere.Thedistinctionwasa13featureofearlytheoriesdescribingthephasesofmatter.Inthenineteenthcentury,forexample,onetheorymaintainedthataliquidcouldbe"dissolved"inavaporwithoutlosingitsidentity,andanothertheory14thatthetwophasesaremadeupofdifferentkindsofmolecules.Thetheoriesnowprevailingtakeaquitedifferentapproachbyemphasizingwhatliquidsandgaseshavein15Theyarebothformsofmatterthathaveno16structure,andtheybothflowreadily.Thefundamentalsimilarityofliquidsandgasesbecomesclearlyapparentwhenthetemperatureandpressureare17somewhat.Supposeaclosedcontainer18filledwithaliquidisheated.Theliquidexpands,orinotherwordsbecomeslessdense;someofitevaporates.Incontrast,thevaporabovetheliquidsurfacebecomesdenserastheevaporatedmoleculesare19toit.Thecombinationoftemperatureandpressureatwhichthedensitiesbecome20iscalledthecriticalpoint.A.addedB.caseC.prominentD.heldE.equalF.partiallyG.exampleH.previous'I.spaceJ,liftedK.permanentL.particularlyM.extendedN.monUnitTwenty-FourPassage2ScientistsatSussexScientistshavefoundthattherearethree13stagesinamosquito'sassault.Stageoneisatfiftyfeetaway,whentheinsectfirstsmellsamanoraanimalto14.Stagetwoisthoughttocomeintooperationabouttwenty-fivefeetfromthetarget,whentheinsectbecomesguidedbythecarbondioxidebreathedoutbytheintendedvictim.Stagethreeiswhenthemosquitoisonlyamatterofinchesfromits15thewarmthandmoisturegivenoffbythevictimisthefinalclue.Theresearchersthen*16howrepellentsinterferewithitsthree-stageattack.Theyfoundrepellentsactmoresubtlythanbyjustgivingoffanastysmell.ACanadianresearchersaysthatrepellentsappearto17mosquitoesfirstwhenitisfollowingthecarbondioxideandsecondduringthefinalapproach,wherethewarmthandmoisturearetheinsect's18.Airpervadedbyoneofthemanychemicalrepellentsstopsthemosquitoreactingtothevictim'scarbondioxide,andtherepellentseemstoaffectthetinyhairswithwhichtheinsectsensesmoistureintheair.Thesensorsareblockedsothatthe19doesnotk