PerhapsthemostsignificantpostwartrendwasthedecentralizationofcitiesthroughouttheUnitedStates，()whenmassivehighway-buildingprogramspermittedgreatersuburbangrowth.
A.and accelerated a phenomenon
B.a phenomenon that accelerated
C.accelerating a phenomenon which
D.the acceleration of which phenomenon
正确答案是B