Final answer:
The question implies a figurative exchange between Andrew Carnegie and John D. Rockefeller, which would be related to their business strategies and dealings. Carnegie was known for his vertical integration in the steel industry, while Rockefeller founded Standard Oil and became a leader in the oil refining business.
Step-by-step explanation:
Andrew Carnegie and John D. Rockefeller
Andrew Carnegie and John D. Rockefeller were two prominent figures of America's industrial age with Carnegie being a steel magnate and Rockefeller an oil tycoon.
Although the question does not specify what exactly they sent to each other, it can be inferred that it is not about literal items they exchanged but rather about the business strategies and approaches both had during their careers.
Carnegie's approach was more focused on vertical integration in the steel industry, owning all aspects of production, from mines to railroads, which enabled him to cut costs and ensure quality.
Rockefeller, on the other hand, made his fortune by refining oil into kerosene and made strategic investments such as the creation of the Standard Oil company.
Both men, however, would have likely exchanged competitive strategies, business insights, and may have even been involved in direct business dealings or negotiations given their prominence and influence in American industry.