Final answer:
Andrew Carnegie specialized in steel production and became a leading steel producer by practicing vertical integration, so option A is correct.
Step-by-step explanation:
Andrew Carnegie specialized in the field of steel production. He rose from humble origins to become one of the leading steel producers in the world.
Carnegie's approach to business was to control every aspect of production, which included direct ownership of mines, foundries, and railroads.
His successful methodology, often referred to as vertical integration, allowed him to lower costs and outcompete other steel companies.
Carnegie Steel became a powerhouse in the industry, with output exceeding that of the entire British Empire by the turn of the century. In his later years,
Carnegie transformed into a major philanthropist, using his enormous fortune to fund libraries, schools, and institutions of higher education.
So, the correct option is A.