Which one of the following best expresses the main idea of the passage? A. United States steel producers face economic problems that are shared by producers in other nations. B. Minimills are the most successful steel producers because they best meet market demands for cheap steel. C. Minimills and specialty-steel mills are more economically competitive than integrated producers because they use new technology and avoid the costs of the iron-smelting process. D. United States steel producers are experiencing an economic decline that can be traced back to the nineteenth century. E. New steelmaking technologies such as continuous casting will replace blast-furnace operations to reverse the decline in United States steel production.