Final answer:
John D. Rockefeller monopolized the oil industry by using horizontal integration and building trusts through his company, Standard Oil, which controlled the vast majority of refineries.The correct answer is option 1.
Step-by-step explanation:
John D. Rockefeller used horizontal integration and the creation of trusts to monopolize the oil industry. His company, Standard Oil, was able to take over or merge with other refineries and controlled about 90% of the nation’s refineries by the 1890s.
This was done through aggressive strategies such as secret deals with suppliers and railroads, and driving competitors out of business by offering lower prices—leading to a reduction in kerosene prices by up to 80% by the end of the 19th century. Rockefeller's methods were heavily criticized by those who suffered under his dominance but were also seen as ingenious by some for streamlining the industry.
The correct option for the industry John D. Rockefeller monopolized is the oil industry (1).