The automobile industry was uniquely suited to the mass production of
American industry during wars required enough of industrial power to outstand other countries. To do this, the automobile industry was specifically equipped with raw materials to manufacture war vehicles such as tanks, jeeps, and trucks. Thus, this industry was uniquely suited to the mass production of 'Military Equipment'.
C is the answer to the question.
Given the fact that the automobile industry was able to produce vast amounts of iron-like products (which were previously cars), they also possessed the capability to produce vast amounts if military equipment as well.