Withouttransportation,therecouldbenotrade.Withouttrade,therecouldbenotownsandcities.Townsandcities aretraditionallythe___16___ofcivilization.Therefore,transportationhelpsmakecivilization___17___.
Throughoutmostoftheprehistoricperiod,peoplelivedbyhunting,fishing,and___18___wildplants.They hadnobeastsofburden,wheeledvehicles,orroads.Peopletraveled___19___andcarriedtheirinfantsand belongingsstrappedtotheirbacksorheads.Loadstooheavyforonepersontocarrywerestrappedtoapoleandcarriedbytwopeople.
___20___,peoplelearnedthattheycoulddragloadsalongthegroundonsledges.Duringlateprehistoric times,peoplebegantobuildsledgeswithrunners. Whenpeopledevelopedagricultureandbegantoestablish___21___settlements,tradebetweensettlements
startedtodevelop,whichcreatedaneedforbetter___22___oftransportation.Thedonkeyandtheox,whichhad beentamedforfoodproductsandfarmwork,helped___23___thisneed.Theuseofdonkeysandoxenasbeastsof burdenenabledpeopleto___24___heavierloadsthantheycouldbefore.
Peoplealsobegantodevelopwatertransportationduringprehistorictimes.Theybuiltraftsofsuch__25____aslogs orreeds.Later,peoplelearned___26___tomakedugoutsandcanoes.Peoplepaddledtheseearlycraftwiththeirhands
orpropelledthemwithpaddlesor__27____.
Thewheelwasinventedabout3500B.C.andsailboatabout3200B.C.Wheeledvehiclesandsailingvessels___28___transportation.Butthespeedoftransportationimprovedonly___29___overthecenturies.Inventorsproducedthefirstengine-___30___vehiclesduringthelate1700’sandtheearly1800’s.This developmentmarkedthebeginningofarevolutionintransportationthathascontinuedtothepresent.
16.A.highlightsB.pinpointsC.headquartersD.centers
17.A.possibleB.acceptableC.practicalD.typical
18.A.growingB.gatheringC.wateringD.moving
19.A.inturnB.ateaseC.onfootD.forfun
20.A.AllthewhileB.ForawhileC.IntimeD.Ontime
21.A.temporaryB.permanentC.regularD.steady
22A.knowledgeB.judgmentC.standardsD.means
23.A.recognizeB.developC.meetD.reduce
24.A.bearB.moveC.shareD.lift
25.A.materialsB.stylesC.itemsD.types
26.A.whereB.whenC.howD.as
27.A.polesB.sailsC.currentsD.winds
28.A.demonstratedB.revolutionizedC.witnessedD.initiated
29.A.considerablyB.continuouslyC.swiftlyD.slightly
30.A.poweredB.controlledC.orientedD.related
2岁内小儿心尖搏动的位置是（）