The correct answer is B) Eastern markets.
The primary function of cowtowns was to link cattle trails with Eastern markets.
During the era of open-range cattle, cows used to roam freely in big portions of land. Cowboys also herded cows throughout long distances. Cowboys took the animals to train stations to be transported to other places to be sold. Cattle were transported to Eastern markets. But this practice ended when farmers put a barbed wire to protect their private properties.
But the era of open-range cattle ranching ended in the West by the 1890s due to the establishment of large farming corporations and barbed wire to protect private property.