Manbuiltrailroadslongbeforehebuiltsteamenginesandbeforehehadevenmasteredthebasictechnologyofengineeringwithironandothermetals.Theearliesttrainswereconstructedoftimberandwereinoperationnotlaterthanthefourteenthcentury.Theywerebuilttoovercometheseverelimita (共 5610 字) [阅读本文] >>