Final answer:
To allay public fears about the safety of the new steel bridge in St. Louis, Andrew Carnegie demonstrated its strength by parading elephants across it, effectively marketing the bridge's safety.
Step-by-step explanation:
Andrew Carnegie was a leading steel producer and a master at promoting and selling his product. To address the public's fear of the new steel bridge in St. Louis and demonstrate its safety, Carnegie orchestrated a highly publicized event where he paraded elephants across the bridge. This was not just a grand spectacle but also a clever marketing strategy, as the sight of these massive animals safely crossing the bridge helped to reassure the public that the structure was indeed strong and sturdy. Carnegie's understanding of public perception and his innovative approach to problem-solving were key factors in the acceptance of steel as a primary material for construction, which was essential to the development of skyscrapers and other steel structures that revolutionize modern cityscapes.