The correct answer is A) the rivers.
The natural feature of Oklahoma that made it easier for traders at Three Forks to transport their goods to markets in the East was the rivers.
The Three Fork area is the region where Arkansas River, Verdigris River, and Neosho River confluence. They are part of Cherokee, Wagoner, and Muskogee counties. It is a transition zone to the Ozark Mountains to the East. In the late 1700s, John Pierre Chouteau had success trading in the area.