The correct response that accurately outlines how John D. Rockefeller was able to monopolize the oil market is B: vertical consolidation - buying/driving out all other oil companies and/or entrepreneurs, and horizontal consolidation - buying into all other industries needed to minimize costs, maximize profits, and dominate the oil market.
This option captures both forms of consolidation that Rockefeller used to achieve his dominance in the oil industry: vertical integration (controlling various stages of production) and horizontal integration (acquiring competitors).