阅读理解Asweallknowmostcountriesintheworlddriveontherightbutthereare75countriesthatdriveontheleftincludingtheUKJapanJamaicaandothers．Whyisthis?I

　　阅读理解

　　Asweallknowmostcountriesintheworlddriveontherightbutthereare75countriesthatdriveontheleftincludingtheUKJapanJamaicaandothers．Whyisthis?

　　Infactsomebelievethatancienttravellersonhorsebackgenerallyrodeontheleftsideoftheroad．Asmostpeopleareright-handedhorsemenwouldthusbeabletoholdthereins(缰绳)withtheirlefthandandkeeptheirrighthandfree－toofferfriendshiptopassingridersortoprotectthemselveswithasword(剑)ifnecessary．

　　ThefirstlawinBritainfortraffictoremainontheleftappearedin1756whichwasrelatedtoLondonBridge．TheHighwayActof1773containedasuggestionthathorsetrafficshouldremainontheleft．TheBritishhadsmallwagons(马车)andthedriverusuallysatontherightsideofthefrontseat．Fromtherehecouldusehislongwhip(马鞭)inhisrighthand．Inthatpositionontherightsideofthewagonthedrivercouldmakesurehiswagonandthepassingtrafficwerebothsafebykeepingtotheleft-handsideoftheroad．

　　CountriesthatbecamepartoftheBritishEmpirefollowedthekeep-leftruletooalthoughthereweresomeexceptions．InCanadaforexampleVancouverandothercoastalprovinceschangedtotherightinordertomakebordercrossingstoandfromtheUnitedStateseasier．DuringWorldWarIIAmericantruckmakersFordChevroletandChryslerbuilt"CanadianMilitaryPattern"trucksforusethroughouttheBritishEmpireandmosttruckswereright-hand-drive．

　　(1)

　　Thefirstparagraphmainlyservesasa(n)________．

　　[]A．

　　background

　　B．

　　conclusion

　　C．

　　introduction

　　D．

　　explanation

　　(2)

　　Ancienthorseridersrodeonthelef