The spread of railroad networks throughout the united states during the 19th century contributed to which of these trends? declining population westward expansion decreased transport costs consolidation of industry

Which of the following describes an effect of world war ll on the united states economy a. automobile companies produced a record number of cars b. many factories had to expand to produce military equipment c. the airplane industry suffered as the allies began using airplanes in combat d. cities with shipyards declined because so many ships had been sent overseas.