What business structure allowed a monopoly over the american oil industry

The correct answer is D) a trust.

The business structure allowed a monopoly over the American oil industry was a trust.

A trust is a fiduciary relationship between a trustor and the trustee. The trustor gives the trustee the right to hold title to assets that benefit a third party. During the Gilded Age, many Americans and American companies became very rich creating monopolies. They bought other companies and practically they had no competition at all. That was the case of John Rockefeller and the Standard Oil Company, or Daniel Carnegie and the Steel Company.

The other options of the questions were A) a corporation, B) a union, and C) a cooperative.