thE FACt thAt mostAmEriCAns livE in urBAn ArEAs DoEs not mEAn thAt thEy rEsiDE in thE CEntEr oF lArgE CitiEs. in FACt, morEAmEriCAns livE in thE suBurBs oF lArgE mEtropolitAn ArEAs thAn in thE CitiEs thEmsElvEs. thEBurEAu oF thECEnsus rEgArDs Any ArEA with morE thAn 2,500 pEoplE As An urBAn ArEA, AnD DoEs not ConsiDEr BounDAriEs oF CitiEs AnD suBurBs. ACCorDing to thEBurEAu, thE politiCAl BounDAriEs ArE lEss signiFiCAnt thAn thE soCiAl AnD EConomiC rElAtionships AnD thE trAnsportAtion AnD CommuniCAtion systEms thAt intEgrAtE A loCAlE. thE tErm usED By thEBurEAu For An intEgrAtED mEtropolis is An msA, whiCh stAnDs For mEtropolitAn stAtistiCAlArE A、in gEnErAl, An ms A、is Any ArEA thAt ContAins A City AnD its surrounDing suBurBs AnD hAs A totAl populAtion oF 50,000 or morE. At thE prEsEnt timE, thEBurEAu rEports morE thAn 280 msAs, whiCh togEthEr ACCount For 75 pErCEnt oF thE u.s. populAtion. in ADDition, thEBurEAu rECognizEs 18 mEgApolisEs, thAt is, Continuous ADjACEnt mEtropolitAn ArEAs. onE oF thE most oBvious mEgApolisEs inCluDEs A ChAin oF hunDrEDs oF CitiEs AnD suBurBs ACross 10 stAtEs on thEEAstCoAst From mAssAChusEtts to virginiA, inCluDingBoston, nEw york, AnD wAshingtonD、 C、in thEEAstErnCorriDor, As it is CAllED, A populAtion oF 45 million inhABitAnts is ConCEntrAtED、AnothEr mEgApolis thAt is growing rApiDly is thECAliForniA CoAst From sAn FrAnCisCo through losAngElEs to sAnDiEgo. ACCorDing to thEBurEAu oF thECEnsus, whAt is An urBAn ArEA A、 A、ChAin oF ADjACEnt CitiEs. B、An ArEA with At lEAst 50,000 pEoplE. C、thE 18 lArgEst CitiEs. D、An ArEA with 2,500 pEoplE or morE.