Final answer:
Andrew Carnegie's steel company operated in an oligopoly and used vertical integration as its business strategy. The company's business organization was a corporation.
Step-by-step explanation:
Andrew Carnegie's steel company operated in an oligopoly, a market structure characterized by a few large firms dominating the industry. Carnegie practiced vertical integration by owning all aspects of production, including mines, freighters, and railroads. This allowed him to cut costs and ensure quality control. The business organization of Carnegie's steel company was a corporation, specifically the United States Steel Corporation created by J.P. Morgan.