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Which choice best describes the function of the underlined sentence in the text as a whole? In 1801, a Blackfoot chief named Ac Ko Mok Ki drew a finely detailed map of the Upper Missouri region. This work demonstrates a vast amount of topographic knowledge, as the map features specific names of mountains and rivers, as well as the first-known sketch of the drainage network of the Missouri River. The map is especially notable because Ac Ko Mok Ki also included details about the numerous tribes that lived in the area.