Homingpigeonisusefulasa______carrierbecausewhentakenfromhome,itwillreturnatthefirstopportunity.

Whilecrossingthemountainarea,allthemencarriedgunslestthey______bywildanimals.

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

The hosts apologized for ______ that some of their guests might be vegetarians.

Wehavetowaitforthebus,______?