Answer :
The answer is C) The company became the only source of steel after competitors went out of business.
The correct answer is Option A) The company controlled every step of steel production, from raw materials to distribution.
A simple monopoly is when one company is able to a majority of the market share for a product. A vertifical monopoly is when a company is able to develop and maintain a monopoly in the market by controlling the complete supply chain of a particular product.
Carnegie Steel was able to do just that, and due to it's sheer size was able to save huge costs on raw materials, helping it to grow and maintain its monopoly of the market.