Rockefeller was able to build his monopoly across the oil industry because he bought up oil refineries, cut costs and reinvested his profits in other refineries.
<h3>Who is John Rockefeller?</h3>
He was the owner of Standard Oil Company and also became one of the world's wealthiest men because of his oil business dominance.
He was able to build his monopoly across the oil industry because he bought up oil refineries, cut costs and reinvested his profits in other refineries.
Therefore, the Option A is correct.
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