Question

how did john d. rockefeller horizontally integrate his monopoly in 1882?
he purchased iron mines around the country to add to his business.
he created a trust that controlled oil wells, refineries, and distribution networks.
he created a trust that controlled ninety percent of the nations oil refineries.
he purchased coal plants around the country to add to his business.

Explanation:

Horizontal integration involves acquiring or merging with competitors in the same industry. Rockefeller's trust controlling 90% of oil refineries (same industry - oil refining) is horizontal integration. Purchasing iron mines/coal plants (different industries) is vertical or conglomerate. Controlling oil wells, refineries, distribution (different stages - vertical).

Answer:

He created a trust that controlled ninety percent of the nation’s oil refineries.