《阅读理解特训:3真2模含解析》2014届高三英语二轮突破11C6[2013·重庆卷]CAlmosteverymachinewithmovingpartshaswheels,yetnooneknowsexactlywhenthefirstwheelwasinventedorwhatitwasusedfor
Wedoknow,however,thattheyexistedover5,500yearsagoinancientAsia
Theoldestknowntransportwheelwasdiscoveredin2002inSlovenia
Itisover5,100yearsold
Evidencesuggeststhatwheelsfortransportdidn'tbecomepopularforawhile,though
Thiscouldbebecauseanimalsdidaperfectlygoodjobofcarryingfarmingtoolsandhumansaround
Butitcouldalsobebecauseofadifficultsituation
Whilewheelsneedtorollonsmoothsurfaces,roadswithsmoothsurfacesweren'tgoingtobeconstructeduntiltherewasplentyofdemandforthem
Eventually,roadsurfacesdidbecomesmoother,butthisdifficultsituationappearedagainafewcenturieslater
Therehadbeennoimportantchangesinwheelandvehicledesignbeforethearrivalo