WhenColumbusreachedtheNewWorld,cornwasthemostwidelygrownplantintheAmericas.Thisplant‘srangeextendedfromwhatisnowsouthernCanadatolowerSouthAmerica.Atthattimesometribescultivateditatsealevel,othersatelevationofmorethan11,000feet.
"Columbushadnowayofknowingthatcornwasfarmorevaluablethanthespices(香料)andgoldhehadhopedtofind."saidFrancesB.King,aprofessoratauniversityofPittsburgh.Throughhumanintervention,thisplanthasdevelopedintoseveralhundredraces,orvarieties.Theirheightsvaryfrom2to12feet,andtheirmaturityrangesfromlittlemorethan2monthstoalmostayear.Theirearsvarynotonlyincolor,butalsoinsize.
Unlikeothercereals(谷类),cornbearslittleresemblancetoitswildancestors.Infact,itdiffersfromtheappearanceofitsimmediateancestorsmorethananyothercultivatedplantknown.Fromhumbleoriginsasalowlandgrass,corndevelopedintothewesternworld‘simportantgrain.Asitshighyieldsallowedcommunitiestogrowfarbeyondwhatearlyagriculturecouldfeed,mostscientistsviewedcornashavinglargelyfueledpre-Columbiangrowthandcivilization.
Now,newfindingsaregreatlyalteringresearchers‘notionsaboutthetimewhencornrevolutionoccurred.NewdatesforitsemergencefromMesoamenricadonotsupportthewidelyheldview.TheevidencenowsuggeststhatthesignsofcorninAmericascandateback5,500yearsatleast.
31.Thefirstparagraphstatesthatcorn（）.
A.wasmainlygrownatsealevel
B.wasnotgrownbelowtheelevationof11,000feet
C.waswidelygrowninCanadaonly
D.spreadthroughoutAmericas
32.Thesecondparagraphimpliesthat（）.
A.thepurposeofColumbus‘explorationwastodiscovercorn
B.cornwasoneofColumbus‘discoveries,butmorepreciousthananythingelse
C.ColumbusknewcornsowellthathebroughtbacktoEuropeatonce
D.cornwastheonlyColumbus‘discoverythatwasremembered
33.Accordingtothepassage,somevarietiesofcorncan（）.
A.ripenlittlemorethan2months
B.lastlittlemorethan2months
C.stayfreshforalmostayear
D.stayalivefrom2monthstoalmostayear
34.Cornhelpedtheearlycommunitiestogrowbecause（）.
A.itwaseasytodigestB.ithadalotofvarieties
C.itcouldproducehighyieldsD.itcouldlastlong
35.Thewidelyheldviewwaschallengedby（）.
A.anewrevolution
B.newfindingsaboutcorn
C.thesignsofcorn5,500yearsago
D.newdatesforcommunities‘emergence