How did john d. rockefeller gain control of the oil industry

In 1870, he established Standard Oil, which by the early 1880s controlled some 90 percent of U.S. refineries and pipelines. Critics accused Rockefeller of engaging in unethical practices, such as predatory pricing and colluding with railroads to eliminate his competitors, in order to gain a monopoly in the industry.

Explanation:

the answer is either c or d i think its d