The location of the Chattahoochee River most significantly contributed to the development of trade in Georgia as described in option C: "It allowed Columbus to become a thriving cotton-marketing center with unobstructed river travel to the Gulf of Mexico."
The Chattahoochee River provided an important means of transportation for goods, particularly during the time when cotton was a major cash crop. Its navigability facilitated trade and commerce in various cities along the river, connecting Georgia's agricultural heartland with broader markets.
While Atlanta also benefited from nearby rivers for trade, it primarily developed as a rail center rather than a river port. Therefore, options B and D are less accurate. Option A, while touching on development, does not specifically address trade and its economic implications.