单选题 .  ①Many scholars have argued that government investment in manufacturing in the southern United States during the Second World War spurred a regional economic boom that lasted into the postwar period. ②But much of this investment went to specialized plants, many of them unsuitable for postwar production. ③Large-scale, wartime government funding led to a massive increase in the number and scale of munitions facilities. ④By the war's end, 216 munitions establishment costing more than $3.5 billion had been built, many of them located in the south. ⑤Indeed, according to one estimate, more than 70 percent of federally financed manufacturing construction capital in Alabama, Arkansas, Mississippi, and Tennessee went into munitions plants.
    ①Even in the northern regions with strong prewar manufacturing economics, these plants were difficult to deal with once the imperative of war had been removed. ②In the south few industrialists had the capacity or desire to transform these factories to a peacetime function. ③Accordingly, at war's end almost all of the southern munitions facilities were shut down, placed on standby, operated at a very low capacity, or converted to nonmanufacturing functions, usually storage. ④Although some reopened a few years later for use during the Korean War, the impact of the special plants on the South's postwar economy was marginal at best.35.  The primary purpose of the passage is to ______