Answer:
The growth of the steel industry and cotton mills in the South in the late 1800s suggests option D: A new approach to the economy was developing in the South.
During this period, the South underwent significant economic changes and diversification. The expansion of the steel industry and the establishment of cotton mills indicated a shift towards industrialization and the development of new economic sectors. This transition represented a departure from the predominantly agrarian and plantation-based economy that had characterized the South prior to the Civil War.