Almosteverymachinewithmovingpartshaswheelsyetnooneknowsexactlywhenthefirstwheelwasinventedorwhatitwasusedfor.Wedoknowhoweverthattheyexistedover5500yearsagoinancientAsia.

Theoldestknowntransportwheelwasdiscoveredin2002inSlovenia.Itisover5100yearsold.Evidencesuggeststhatwheelsfortransportdidn’tbecomepopularforawhilethough.Thiscouldbebecauseanimalsdidaperfectlygoodjobofcarryingfarmingtoolsandhumansaround.

Butitcouldalsobebecauseofadifficultsituation.Whilewheelsneedtorollonsmoothsurfacesroadswithsmoothsurfacesweren’tgoingtobeconstructeduntiltherewasplentyofdemandforthem.Eventuallyroadsurfacesdidbecomesmootherbutthisdifficultsituationappearedagainafewcenturieslater.Therehadbeennoimportantchangesinwheelandvehicledesignbeforethearrivalofmodemroaddesign.

Inthemid-1700saFrenchmancameupwithanewdesignofroad—abaselayer(层)oflargestonescoveredwithathinlayerofsmallerstones.AScotsmanimprovedonthisdesigninthe1820sandastronglastingroadsurfacebecameareality.Ataroundthesamelimemetalhubs(thecentralpartofawheel)cameintobeingfollowedbythepneumatictyre(充气轮胎)in1846.Alloywheelswereinventedin1967sixtyyearsaftertheappearanceoftarmackedroads(柏油路).Aswheeldesigntookoffvehiclesgotfasterandfaster.

1.Whatmightexplainwhytransportwheelsdidn’tbecomepopularforsometime?

A．Fewknewhowtousetransportwheels.

B．Humanscarriedfarmingtoolsjustaswell.

C．Animalswereagoodmeansoftransport.

D．Theexistenceoftransportwheelswasnotknown.

2.Whatdoweknowaboutroaddesignfromthepassage?

A．Itwaseasierthanwheeldesign.

B．Itimprovedafterbigchangesinvehicledesign.

C．Itwaspromotedbyfast-movingvehicles.

D．Itprovidedconditionsforwheeldesigntodevelop.

3.Howisthelastparagraphmainlydeveloped?

A．Bygivingexamples.

B．Bymakingcomparisons.

C．Byfollowingtimeorder.

D．Bymakingclassifications.

4.Whatisthepassagemainlyabout?

A．Thebeginningofroaddesign.

B．Th