ThefirstimportantexpositionintheUnitedStateswasheldinPhiladelphiain1876.
A、exhibitionThewheelsofthefirstroadvehicleswerefashionedfromcrudestonedisks.
In1861itseemedinevitablethattheSouthernstateswouldbreakawayfromtheUnion.
InthenortheasternUnitedStates,itrainsintermittently间歇地throughoutthespring.
ThefuturesurvivalofthebaldeagleisstillanimportantAmericanecologicalconcern.
Urbanrenewalprogramsstrivetoupgradeareasthatarebecomingslums.