Final answer:
John D. Rockefeller responded to the loss of his customers in the oil industry through horizontal and vertical integration.
Step-by-step explanation:
John D. Rockefeller responded to the loss of his customers in the oil industry by practicing horizontal integration and vertical integration. He merged with other oil companies and underpriced his competitors to dominate the market, using his vast power to drive them out of business. He also invested in other industries and acquired companies involved in various aspects of the oil production process. Through these strategies, he consolidated almost all oil refining businesses in the country and controlled 90 percent of the world's refining businesses.