A--automobile assembly plants would have been found in the "Steel Belt" which includes Michigan, Illinois, Indiana, Ohio, Kentucky, Pennsylvania, and West Virginia.
B--plants are still in the same areas. The majority being in Michigan. There are more variety of the plants due to increases in companies.
C--with increased power sources and transportation, the plants could be more to other locations. Many have decreased or the plants have changed leaving the 'steel belt' to now be referred to as the 'rust belt'.