Question

by means of a ____, rockefeller came to own more than 90% of americas oil industry. standard oil thus became a monopoly - a single company that controlled virtually all the u.s. oil production and distribution.
trust
referendum
recall
initiative

Explanation:

Standard Oil under Rockefeller became a monopoly by creating a trust, which allowed it to control a vast majority of U.S. oil production and distribution. A trust is a legal - financial arrangement where multiple companies are consolidated under a single management for the purpose of eliminating competition and gaining market control.

Answer:

D. Trust