北外雅思2013年10月真題解析及11預測

Whydidthetwostudentschooseyoungerchildren?A.Becausetheywillgotoworkwiththem.Whatpreparationhavetheydone?B.TheyhavedonesomeclassroomWhydidtheyusetheopenquestionsbutnotclosedquestionsin A.Becauseresultsfromtheopenquestionswillbemore24.Whatshouldtheydoaftertheyfinishedit?C.Theyshouldlettheprofessorcheck25.Whatshouldtheydonext?C.Theywillgotofindacollege26-3026.27.ing:encourageteacherstoteachQuestionnaire:reflectteachers’trueReadingarticlesandbooks:otherstudentsalsowillhavedoneWebsearching:usefulskillforfuture31-40Workersand eshigh-saltybecause:Innocence Workersareeasytobehurtbecausethelackof:protectiveUserainwatertoDesignerinspiredby2011.8.13過 Australiancanesugar4，了的XX走了，剩下一大把人在考慮何去何從，然后有專家先說了種甘蔗和可是并沒有收到很好的收益，制糖工業(yè)的將會成為最終的結(jié)局。F配對題第一個選的是Tom有關financialTomAbout800millionAUdollars(801millionU.S.dollars)inprofitfromsugarcanecropshasbeenwashedawaybytorrentialdownpoursalongAustralia'seasternseacoastin2010,sugarproducerssaidonThursday.Australia'ssugarcaneindustrygroupCanegrowerssaidgrowersstartedtheyearasworldpricesrosetotheirhighestlevelin30years,butheavyrainsontheeasternseaboardwashedawayhopesofarecordseason.Thegroupsaidtheextraordinarydownpoursmadethesugarcontentinthecanelow,makingitlessprofitabletomill.Boggyfieldsmeantharvestingmachinerycouldnotbeused,leavingupto18percentofthecropunharvested,Canegrowerssaid.Thegroupsaidwetpaddocksleftgrowersunabletorentnextseason'squota,addingtootherproblemsthatwouldalsoseelowerprofitsin2011.InthePapales'caseitmeantmovingawayfromtheoldparadigmoftryingtogrowmuchcaneonasmuchareaastheyTheysacrificedfourhectarestocreateanartificialwetlandinthemiddleoftheirfarmthatservestotraprun-offfromtheircanefieldsinsteadofitendingupouttosea.Theworkwascarriedoutunderthefirstphaseofthe$200millionReefRescueProgram-acollaborativedealbetweenernmentandgrowersaimedatminimisingnutrientandchemicalfarmrun-offandimprovingwaterqualityonthereef."Foreverydollartheernmentputup,wespent$1.80andmultiplythatbytheotherlocalgrowerswhoputtheirhandupandthetotalinvestmentwashuge,"MrPapale"We'vehadsomereallywetweathersincewebuiltit,andit'shelpedthefarmdrainnaturally–withoutpum,whichhelpsthehippocket–andmoreimportantlycontainsthatrunoffrighthere,"hesaid."Andwhat'smorethere'sbeennonegativeimpactoneitherourproductivityorprofitability."MrPapalesaysheisproudofwhatheisng."Thispieceofdirthassustainedmyfamilyforfourgenerations,soweareobviouslyngsomethingright,"hesaid.2008.11.15過81TheLostCityThelowgranitemountain,knownasKerkenesDag,jutsfromthenorthernedgeoftheCappadocianininTurkey.Sprawledoverthemountainsidearetheruinsofanenormouscity,containedbycrumblingdefensivewallssevenkilometerslong.ManyrespectedarchaeologistsbelievethesearetheremainsofthefabledcityofPteria,thesixth-centuryBCstrongholdoftheMedesthattheGreekhistorianHerodotusdescribedinhisfamousworkTheHistories.Theshort-livedcitycameunderMediancontrolandonlyfiftyyearslaterwassacked,burnedanditsstrongstonewallsdestroyed.BritisharcheologistDrGeoffreySummershasspenttenyearsstudyingthesite.Excavatingtheruinsisachallengebecauseofthevastareatheycover.The7kmperimeterwallsrunaroundasitecovering271hectares.DrSummersquicklyrealiseditwouldtakefartoolongtoexcavatethesiteusingtraditionaltechniquesalone.Sohedecidedtousemoderntechnologyaswelltomapentiresite,bothaboveandbeneaththesurface,tolocatethemostinterestingareasandprioritiestostartdigging.In1993,DrSummershiredaspecialhand-heldballoonwitharemotecontrolledcameraattached.Hewalkedovertheentiresiteholdingtheballoonandtakingphotos.Thenoneafternoon,herentedahot-airballoonandfloatedoverthesite,takingyetmorepictures.Bytheendofthe1994season,DrSummersandhisteamhadajigsawofaerialphotographsofthewholesite.Thenextstagewastouseremotesensing,whichwouldletthemworkoutwhatlaybelowtheintriguingoutlinesandruinedwalls.“Archaeologyisadisciplinethatlendsitselfverywelltoremotesensingbecauseitrevolvesaroundspace,”saysScottBranting,anassociateddirectoroftheproject.HestartedworkingwithDrSummersin1995.Theprojectusedtwomainremote-sensingtechniques.Thefirstismagnetometry,whichworksontheprinciplethatmagneticfieldsatthesurfaceoftheEarthareinfluencedbywhatisburiedbeneath.Itmeasureslocalisedvariationsinthedirectionandintensityofthismagneticfield.“TheEarth’smagneticfieldcanvaryfromcetoce,dependingonwhathappenedthereinthepast,”saysBranting.“ifsomethingcontainingironoxidewasheavilyburnt,bynaturalorhumanactions,theironparticlesinitcanbepermanentlyreoriented,likeacompassneedle,toalignwiththeEarth’smagneticfieldpresentatthatpointintimeandspace.’Themagnetometerdetectsdifferencesintheorientationsandintensitiesoftheseironparticlesfromthepresent-daymagneticfieldandusesthemtoproduceanimageofwhatliesbelowground. KerkenesDaglendsitselfparticularlywelltomagnetometrybecauseitwasallburntatonceinasavagefire.Incestheheatwassufficienttoturnsandstonetoglassandtomeltgranite.ThefirewassohotthattherewerestrongmagneticsignaturessettotheEarth’smagneticfieldfromthetime547BC-resultinginextremelyclearpictures.Furthermore,thecitywasneverrebuilt,“ifyouhavemultiplelayersconfusingpicture,becauseyouhavedifferentwallsfromdifferentperiodsgivingsignaturesthatallgoindifferentdirections,”saysBranting.“Weonlyhaveonegoingdownabout1.5meters,sowecangetagoodpictureofthisfairlyshort-livedcity.”FTheothermainsub-surfacemaptechnique,whichisstillbeingusedatthesite,isresistivity.Thistechniquemeasuresthewayelectricalpulsesareconductedthroughsub-surfacesoil.It’sdonebyshootingpulsesintothegroundthroughathinmetalprobe.Differentmaterialshavedifferentelectricalconductivity.Forexample,stoneandmudbrickarepoorconductors,butlooser,dampsoilconductsverywell.Bywalkingaroundthesiteandtakingaboutfourreadingspermetre,itispossibletogetadetailedideaofwhatiswherebeneaththesurface.Theteamsthenbuilduppicturesofwalls,hearthsandotherremains.“Ithelpsalotifithasrained,becausetheelectricalpulsecangetthroughmoreeasily,”saysBranting.“Thenifsomethingismoreresistant,itreallyshowsup.”Thisisoneofthereasonsthattheprojecthasaspringseason,whenmostoftheresistivityworkisdone.Unfortunay,resistivityisalotslowerthanmagnetometry.“Ifwedidresistivityoverthewholesiteitwouldtakeabout100years,”saysBranting.Consequently,theteamisconcentratingonareaswheretheywanttoclarifypicturesfromthe RemotesensingdoesnotrevealeverythingaboutKerkenesDag,butitshowsthemostinterestingsub-surfaceareasofthesite.Thearchaeologistscanthenexcavatetheseusingtraditionaltechniques.Onesurprisecamewhentheydugoutoneofthefatesinthedefensivewalls.“Ourobservationsinearlyseasonsledustoassumethatwewerelookingatastonebasefromamudbrickcitywall,suchaswouldbefoundatmostothercitiesintheAncientNearEast,”saysDrSummers.“Whenwestartedtoexcavatewewerestaggeredtodiscoverthatthewallsweremadeentirelyfromstoneandthatthegatewouldhavestoodatleasttenmetreshigh.Aftertenyearsofstudy,PteriaisgivingupitsReadingPassage2hassevenparagraphs,A-G.Whichparagraphcontainsthefollowinginformation?14Thereasonwhyvariousinvestigativemethodsare15Anexampleofanunexpected16Themethodstosurveyedthesurfaceofthesitefrom17ThereasonwhyexpertswanttostudytheExploringtheAncientCityofTherelevantworkwasdonetenyearsago.Tobeginwith,expertstookphotosofthesitefromthegroundandthenfromadistanceina18 .Tofindoutwhatlaybelowthesurface,theyusedtwoleadingtechniques.Onewasmagnetometer,whichidentifieschangesinthemagneticfield.Thesechangesoccurwhenthe inburiedstructureshavechangeddirectionasaresultofgreatheat.Theymatchwiththemagneticfield,whichissimilartoa20 .Theotheronewasresistivity,whichusesa21 tofireelectricalpulsesintotheearth.Theprincipleisthatbuildingmaterialslike22 andstonedonotconductelectricitywell,while23 doesthismuchbetter.Archaeologistspreferredtousethistechniqueduringthe24 ,whenconditionsaremorefavourable.Resistivityismainlybeingusedto25 someimagesgeneratedbytheChoosethecorrectletter,A，B,CorHowdomodernremote-sensingtechniqueshelpattheATheyavoidtheneedforexpertstodiganypartoftheBTheybringpartsofthesiteintolightsothatkeyareascanberesearchedCTheyshowminuteburiedobjectsforthearchaeologiststodigDTheymaketheinvestigationmoreflexibleastheycanbeusedatanytimeof14-17BGC18.hot-air19.iron23.looserdamp26.新Savethe54，CurrentlythereisinexcessofseventyspeciesoflizardsrecognisedinNewZealand,allbelongingtooneoftwofamilieseithergeckosorskinks.Worldwidethereareabouttwentysixfamiliessuchasmonitors,dragonschameleonsetc.Someofthedifferencesinthetwofamiliesareasfollows:Astheirscalesoverlapskinkstendtohaveasmoothglossyappearancewhileingeckosthescalesdonot,givingthemamorevelvetyormattfinish.TheOtagoSkinkisoneofNewZealand'srarestandlargestskinks.Theyhavebeendecimatedbypredatorsandarepredictedtobeextinctinthewildby2012.Theyarereducedto8%oftheirformerrange.Theirmarkingprovidesexcellentcamouflageonthelichencoveredrocksoftheirnaturalhabitat.TherecoverynfortheOtagoskinksandgrandskinkshastakenadifferentpathtorecoverynsdevelopedforotherNewZealandthreatenedspecies.Thisacknowledgesafundamentaldifferencebetweenthespeciesdiscussedinthisnandallotherspeciesrecoverynsdevelopedsofar:allremaininghabitatsoftheOtagoskinksandgrandskinksoccuronholdorCrownrenewableleaseholdland.Clearly,beforeproceedingwithfullpublicconsultationovertherecoveryactionsproposedforthesespecies,ithasbeennecessarytocloselyinvolvelandownersinthedevelopmentofthenandtoallayanyconcernstheymayhaveabouttheactionsproposedinthedraftrecoveryn.TheOtagoskinkandthegrandskinkaretwoofNewZealand'srarestlizards.areknownonlyfromOtago,andbothspeciesarecurrentlyregardedasvulnerablebyIUCNstandards.TheyareamongstthelargestofNewZealandlizards,upto250-300mmlong.Theymatureintheirthirdor yearandgivebirthto2-4young.Theyarestronglydiurnalandeatawidevarietyofinvertebratesandfruit.Thesespeciesarerock-dwellingandalmostinvariablyoccuronschistoutcrops,theirpreferredhabitatbeinglarge,well-crevicedoutcropsamidsttussockgrasslandorindigenousFormerlywidespreadinCentralOtagoataltitudesbetween200-1000mtheyarefoundoveronlyabout8%oftheirpastrange.Thetwo,widely-spacedpopulationgroupsare:(intheeast)betweenHyde,MacraesFlat,SuttonandPukerangi,butmostcommonintheheadwatersoftheWaikouaitiRiverandNenthornStream,and(inthewest)intheLindiscatentandatonesitenearLakeHawea.Thereasonsforconcernarethelizards'diminishedrangeandcontinuallydecliningpopulations,andthefactthatmanypopulationsarenowextremelysmallandisolated.Thecausesfordeclinearenotpreciselyknownbutincludehabitatdegradationanddestruction(primarilyfromagriculturaldevelopment),predationbyintroduced lsandbirds,andpestcontroloperations.Allofthesefactorsarestillineffectandthreatenthesurvivaloftheremainingpopulations.Changingfanningpracticesandnewpestcontrolmethodsincreasetheriskstolizards,particularlyastherearenoreservesinwhichtheirhabitatisprotected.SeveralfeaturesofthebiologyofOtagoskinksandgrandskinksmakethemparticularlyvulnerabletoextinction.Theseincludelate ualmaturity,lowproductivity,largesize,highlyspecifichabitatrequirements,smallandisolatedpopulations,andthefactthattheirdistributionislimitedtothe.Nevertheless,thefacttheyoccuroverawidegeographicrange,arestillrelativelynumerouswithhighpopulationdensitiesatsomelocalities,andarebreedinginthewildsuggeststhatinsinuprotectionisfeasibleandcouldwellincreasetheirchancesofsurvival.Captivemaintenanceandbreedingispossibleandcouldbeimplementedifnecessaryfortheskinks'conservation.ThemostfavouredoptionfortheconservationofOtagoskinksandgrandskinksispreservationinsitubyprotectingtheirhabitat.Thiscanbeachievedthroughatwo-tieredprogrammeofhabitatprotectionbytheDepartmentofConservationand/orvoluntarypreservationagreementsbylandowners.SitestobeprotectedbytheDepartmentwillbechoseneitherbecausetheyarecoreareasfortheconservationofthesespecies(onthebasisofthequalityanddensityofthelizardpopulationstheycontainandthepotentialforthemaintenanceorenhancementofthesepopulations)orbecausethepopulationsarcnearthelimitsofdistribution.Sitesforcooperativemanagementwithlandownersshouldpreferablyfulfilthesamecriteria.IthastobeacceptedthatitisnotphysicallyorfinanciallypossibletoprotectallremainingpopulationsofOtagoskinksandgrandskinksandthat,nomatterhowsuccessfultheconservationprogrammeis,manywilldieout.Otherproblemsfortherecoveryprogrammearethepresentlackofinformationontheecologyofthespecies,howtheirhabitatmaybemaintainedorenhanced,andonmanagementofvisitorstokeysites.Itisimportant,forsuccessoftherecoveryprogramme,toimplementaresearchprogrammeassoonaspossible.Highprioritiesare:develoappropriatecapture,markingandmonitoringtechniques;comparingthegeneticstatusoftheeasternandwesternpopulations;studyingspecifiedaspectsofthespecies'ecology;anddeterminingtheeffectsdifferentlandmanagementpractices,pestcontroloperationsandpredatorcontroloperationshaveonlizardpopulations.Itisalsoimportanttoinvestigateanyreportsofthesespeciesfrombeyondtheirknownrange.Contactwithallrelevantlandownersistobemadeattheearliestopportunitytoensuretheyarefullyinformedoftherecoverynanditsimplications.Landowners'viewswillbesoughtthroughouttheprogramme,andappropriatemanagementobjectiveswillbesetafterthisconsultation.ConservationMinisterSteveChadwicktodayannouncedamajorconservationmanagementandresearchbreakthroughwithgrandandOtagoskinks,andacaptivebreedingprogrammewithOtagoSkinks,aimedatsecuringthegeneticdiversityofthespecies.“GrandandOtagoskinksareNewZealand’slargestlizardsandarecriticallyendangered,alongwithkakapoandMauisdolphin.Animportantbreakthroughinpredatorcontrolhasledtoastrongrecoveryinaprotectedpopulationofupto94percentinjustthreeyears,”SteveChadwicksaid.“ThisisthefirsttimeonNewZealandthattherehasbeensuchadramaticrecoveryinacriticallyendangeredspecies.”AtMacraesConservationAreainEasternOtago,twoml-proofexclosuresand45kilometresoftraplineshavebeenusedtocontrolawiderangeofpredators.“TheDepartmentofConservation(DOC)RecoveryProgrammeTeamhasalsodevelopedworldleadingtechniques.TheseadvanceshavenotonlybenefitedgrandandOtagoskinks,butcanbeusedwithotherthreatenedspeciesontheNewZealand.“ThecaptivebreedingprogrammeforOtagoskinksisagreatexampleofcollaborationbetweenagenciesandindividuals,involvingWellingtonZoo,DOCandprivatebreeders.“ThelizardsarefromthewildandhaveonlyrecentlyarrivedatWellingtonzoo’sspecialist,conservationunit.Threeexperienced,privatebreedersinthelowerNorthIslandarealsoinvolved.“TheselizardsareanimportantpartofournationalheritageandIwishthesegroupseverysuccessincaptivityandinthewildtosavethegrandandOtagoskinksfromextinction.”smalllegs,wintersleep,bodyheatlocation,captivity,都在第一段第二題是Y/N/NGThechartbelowshowsthegrowthofpopulationofurbanizationincertainpartsofworldandthepredictionofthedatain要素回憶（圖表參考Thebarchartshowsinformationabouttheurbanpopulationgrowthoftheworldandotherthreeareasfrom1950to2030.Itismanifestthatcitypopulationofalltheceswasincreasingsustainablyandsteadilgenerallyduring1950and2000,anditispredictedthatin2030theurbanpopulationwilaccountforoverhalfofthewholepopulation.TheareasofAfricaandAsiaaresimilar,totalingapproximay25%ofcitydwellerespectivelyin1950,afterwhichin2000itnearlygrewbyalmosthalf.In2030,bothothemaresupposedtoincreasetoabove50%.LatinAmericashowsahigherpercentagecomparedotherpartsandthewholeworld.Startedataround40%in1950,itexperiencedarelativelysteeprise,at70%in2000,whichdoubledtheothertwocesandtheworld.Nosurprisingly,itwillreachthepeakatjustover80%in2030.Synthesizedallthecesinthworld,thetrendofurbanpopulationofthewholeworldascendedgently,withroughly30%45%,60%in1950,2000and2030respectively.Overall,urbanpopulationofthewholeworldandcesshowedanupwardtrendduring1950and2000,andcityresidentsareexpectedtoaccountformorethanhalfofthe考試日期： Somepeoplethinkgivingaidtopoorercountrieshavemorenegativeeffectsthanpositiveeffects.Towhatextenddoyouagreeordisagree?

Itcannotbedeniedthatfinancialdifferenceshavebeenexistingbetweendifferentcountriesasalways.Forthisreason,somepeopleproposethatitisdevelopedcountries’responsibilitytoprovidefinancialaidtothecountriesthatareeconomicallyinferiortothem,whichhasbeencounter-arguedbysomecriticsbelievingthenegativeeffectsofthispracticeoutweighthepositiveones.Admittedly,financialassistanceisanexcellentchanceforapoorcountrytoimproveitsinfrastructureandtheenvironment.Sufferedfromshortageofbasicmaterialsandfacilitietostartbusinesses,itisfundamentaltobesupportedbasicindustryrelatedfactorssuchalight,electricity,load,highways,naturalresources,technologytobeoutofpoverty.Aidinghelppoorcountriesinthissituationcansolvetheireconomicalproblemsandruntheirownbusiness.Furthermore,afterrealizingthehelp,develo countrymight developedandcontributetotheworld.However,thepracticemayalsobringsomeproblemswhichmaypotentiallyresultinseriousnegativeeffects.Initially,thepracticedoesn’tnecessarilyensureadelightingeconomicgrowthintherecipientcountriesasitishighlypossiblethebeneficiarycountrieseover-dependentonthefinancialaidfromtheoutsideandslowdownthestepstodevelopthedomesticeconomyindependently.Anotherpointagainstfinancingdevelosocietiesisthatthereisabigrisktoencounterwithcorruptionsisthehighestlevelsoauthority.Aftergettingassistancecitizensdonotfeelandseepositivechangesinfrastructureisnotimproved.Imeanthatfundsextractingfordevelopmentarelostinsomeone’spockets.Forexample,afterastorminPakistan,thereappearedafoodandhousecrisisneverthelesstheEUsenthumanitarianhelp.Mostimportantly,aftergettingasignificantloanacountrymightlosetheirpolitical domandbedependentuponaTosummarize,Iconsideraidforneededcountriesbringsmorenegativeimpactsthanprofit.Inmy ,theaidisnotconstitutedonlyfrommoney.Itcanbesomeeducationalprograms,medicineandscientificresearches.Part2&ParthouseorAninterestingcountry/AcountryyouAsubjectyoudislikemostinmiddlehometown/livingAdecisionyoutakealongPublicAsubjectyoudislikemostinmiddleapartmentorSport/AwaytokeepAyoumeetAjobyouliketodointheAcharacterfromachildhood2013101220131012?兩新：Section1&4?兩舊：SectionLocationoftheschool:oppositethegolfUniform:blueLessontime:7:20-Activity:***programwasgivenbreakfastbeforeschoolLanguage:daytomeettheprincipal:TimetomeettheprincipalShealsowantstomeetthesciencehomeMultipleChoices/Doesthehostgetpaid?receivenoWhatforeignersdotheybuildfor?thosedifficulttomakeWhatdoestheguestdothere?選discussaboutalWhatisthebenefit?promoteculturaltwophotos,oneforvetting,theotheroneforhosthaveaninterviewwithreceiveacknowledgementwithin7Multiplechoice/ Whatisthebackgroundofthistopicbasedon?選basedonAustralianbesimilartotheoneprojecttheydid ytheresearchmethodis_選thetutorsuggeststhatthesurveyhadbetter_選variousdonotbetoowhatdoesthetutorthinkofusingthedatatable?選trytoThegirlstudentsaystheywillinvestigate15children,andtheywillbedividedinto3groupsaccordingtotheage.Thereare5childrenineverygroup.Thetutorsaysthereisnoneedand_Breducethenumberofreducethenumberofchildrenineach26.Aboutthebackground,_TheyhaveTheydon’thaveenoughtimetodoTheyputitintoanotherHowtoallocatetheAJanedoitB男生DouglasdoitCtheydoittogether一起thefinalreport--theletter--petrolmarketheadfreshPassage2011.1.8GoingT/F/NG判斷題學家表示了自己在不同階段的結(jié)果和觀點。說到了轉(zhuǎn)食品，S打頭的一種Going Theworld’sfavouritefruitcoulddisappearforeverin10years’time.Thebananaisamongtheworld’soldestcrops.Agriculturalscientistsbelievethatthefirstediblebananawasdiscoveredaroundtenthousandyearsago.IthasbeenatanevolutionarystandstilleversinceitwasfirstpropagatedinthejunglesofSouth-EastAsiaattheendofthelasticeage.Normallythewildbanana,agiantjungleherbamassofhardseedsthatmakethefruitvirtuallyinedible.Butnowandthen,hunter-gatherersmusthavediscoveredraremutantntsthatproducedseed-less,ediblefruits.Geneticistsnowknowthatvastmajorityofthesesoft-fruitedntsresultedfromgeneticaccidentsthatgavetheircellsthreecopiesofeachchromosomeinsteadoftheusualtwo.Thisimbalancepreventsseedsandpollenfromdevelonormally,renderingthemutantpopularfruitcouldbedoomed.Itlacksthegeneticdiversitytofi anddiseasesthatareinvadingthebananathesmall-holdingsofAfricaandAsiaInsomeways,thebananatodayresemblesthepotatobeforeblightbroughtfaminetoIrelandacenturyandahalfago.But“itholdsalessonforothercrops,too”,saysE Frison,topbananaattheInternationalNetworkfortheImprovementofBananaan4ntaininMontpellier,France.“Thestateofthebanana”,Frisonwarns,“canteachabroaderlessontheincreasingstandardisationoffoodcropsroundtheworldisthreateningtheirabilitytoadaptandsurvive.”ThefirstStoneAgentbreederscultivatedthesesterilefreaksbyrentingcuttingsfromtheirstems.Andthedescendantsofthoseoriginalcuttingsarethebananaswestilleattoday.Eachisavirtualclone,almostdevoidofgeneticdiversity.AndthatuniformitymakesitripefordiseaselikenoothercroponEarth.Traditionalvarietiesof uallyreproducingcropshavealwayshadamuchbroadergeneticbase,andthegeneswill bineinnewarrangementsineachgeneration.Thisgivesthemmuchgreaterflexibilityinevolvingresponsestodisease-andfarmoregeneticresourcestodrawoninthefaceofanattack.Butthatadvantageisfadingfast,asgrowersincreasinglyntthesamefew,high-yieldingvarieties.ntbreederworkfeverishlytomaintaininthesestandardizedcrops.Shouldtheseeffortfalter,yieldsofeventhemostproductivecropcouldswiftlycrash.“Whensomepestodiseasecomesalong,severeepidemicscanoccur,”saysGeoffHawtin,directoroftheRome-basedInternationalntGeneticResourcesInstitute.Thebananaisanexcellentcaseinpoint.Untilthe1950s,onevariety,theGrosMichel,dominatedtheworld’scommercialbananabusiness.FoundbyFrenchbotanistsinAsianthe1820s,theGrosMichelwasbyallaccountsafinebanana,richerandsweeterthantoday’sstandardbananaandwithoutthelatter/sbitteraftertastewhengreen.ButitwasvulnerabletoasoilfungusthatproducedawiltknownasPanamadisease.“Oncethefungusgetsintothesoilitremainsthereformanyyears.Thereisnothingfarmerscando.Evenchemicalsprayingwon’tgetridofit,”saysRodomiroOrtiz,directoroftheInter-nationalInstituteforTropicalAgricultureinIbadan,Nigeria.Sontationownersyedarunninggame,abandoninginfestedfieldsandmovingso“clean”land-untiltheyranoutofcleanlandinthe1950sandHadtoabandontheGrosMichel.Itssuccessor,andstillthereigningcommercialking,istheCavendishbanana,a19th-centuryBritishdiscoveryfromsouthern.TheCavendishisresistanttoPanamadiseaseand,asaresult,itli savedtheinternationalbananaindustry.Duringthe1960s,itrecedtheGrosMichelonsupermarketshelves.Ifyoubuyabananatoday,itisalmostcertainlyaCavendish.Butevenso,itisaminorityintheworld’sbananaEHalfabillionpeopleinAsiaandAfricadependonbananas.Bananasthelargestsourceofcaloriesandareeatendaily.Itsnameissynonymouswithfood.ButthedayofreckoningmaybecomingfortheCavendishanditsindigenouskin.Anotherfungaldisease,blackSigatoka,has eaglobalepidemicsinceitsfirstappearanceinFijiin1963.Lefttoitself,blackSigatoka-whichcausesbrownwoundsonleavesandpre-maturefruitripeningcutsfruityieldsby50to70percentandreducestheproductivelifetimeofbananantsfrom30yearstoaslittleas2or3.CommercialgrowerskeepSigatokaatbaybyamassivechemicalassault.Fortysprayingsoffungicideayearistypical.Butdespitethefungicides,diseasessuchasblackSigatokaaregettingmoreandmoredifficulttocontrol.“Assoonasyoubringinanewfungicide,theydevelop,”saysFrison.“OnethingwecanbesureofisthattheSigatokawon’tloseinthisbattle.”Poorfarmers,whocannotaffordchemicals,haveitevenworse.Theycandolittlemorethanwatchtheirntsdie.“MostofthebananafieldsinAmazoniahavealreadybeendestroyedbythedisease,”saysLuadirGasparotto,Brazil’sleadingbananapathologistwith ernmentresearchagencyEMBRAPA.Productionislikelytofallby70percentasthediseasespreads,hepredicts.Theonlyoptionwillbetofindanewvariety.Buthow?Almostallediblevarietiesaresusceptibletothediseases,sogrowerscannotsimplychangetoadifferentbanana.Withmostcrops,suchathreatwouldunleashanarmyofbreeders,scouringtheworldforresistantrelativeswhosetraitstheycanbreedintocommercialvarieties.Notsowiththebanana.Becauseallediblevarietiesaresterile,bringinginnewgenetictraitstohelpcopewithpestsanddiseasesisnearlyimpossible.Nearly,butnottotally.Veryrarely,asterilebananawillexperienceageneticaccidentthatallowsanalmostnormalseedtodevelop,givingbreedersatinywindowforimprovement.BreedersattheHonduranFoundationofAgriculturalResearchhavetriedtoexploitthistocreatedisease-resistantvarieties.FurtherbackcrossingwithwildbananasyieldedanewseedlessbananaresistanttobothblackSigatokaandPanamadisease.NeitherWesternsupermarketconsumersnorpeasantgrowerslikethehybrid.Someaccuseitoftastingmorelikeanapplethanabanana.Notsurprisingly,themajorityofntbreedershavetillnowturnedtheirbacksonthebananaandgottoworkoneasiernts.Andcommercialbananacompaniesarenowwashingtheirhandsofthewholebreedingeffort,preferringtofundasearchfornewfungicidesin