Question

What business practice contributed most to Andrew Carnegie’s ability to form a monopoly?
using profits to support charities in order to greatly improving his reputation
increasing his profits every year
focusing on a single aspect of steel production
combining his companies into one company, and controlling all aspects of steel production

Answer 1

combining his companies into one company, and controlling all aspects of steel production

Carnegie built a monopoly through vertical integration and consolidation—owning raw materials, transportation, mills, and distribution—to cut costs and drive competitors out.