Question

John D. Rockefeller started in the oil industry as a business partner in a refinery. How did he become one of the nation's wealthiest men?
He reduced the cost of production by building a huge factory that manufactured equipment for drilling oil.

He created a monopoly that controlled most of the production and transportation of refined petroleum.

He engineered the purchase of Andrew Carnegie's steelmaking empire, and then merged the oil and steel industries.

He encouraged competition in the oil industry so that technology would remain efficient and cost effective.