Which practice involved pooling resources among railroads to fix shipping rates?

The correct answer is pools. This term specifically refers to agreements among railroad companies to share resources and establish uniform shipping rates in order to limit competition and stabilize their profits. By pooling their resources, these companies could effectively coordinate their pricing strategies without directly competing against one another, which often led to increased earnings for each participating railroad.

In the context of the late 19th century, this practice was a common response to the intense competition that railroads faced, as companies sought ways to ensure profitability. Instead of competing fiercely on price, pooling allowed companies to collaborate, which often resulted in higher rates for shippers as well.

Trusts, monopolies, and syndicates refer to different organizational structures or strategies within the broader context of business practices aimed at controlling markets or industries. Trusts usually involve a central entity managing multiple companies, monopolies refer to the dominance of a single company over a market, and syndicates typically involve a group of individuals or companies that co-operate for mutual benefit but not specifically focused on rate-setting like pools. Thus, pools is the most accurate term for the described practice.