单选题 .  ①George Milner cites three primary problems with the labeling of Cahokia, the large archaeological site by the Mississippi River, as a state rather than a chiefdom. ②First, finds at Cahokia are essentially similar to finds at other Mississippian chiefdoms, except that the amount of earth moved in building the mounds at Cahokia was greater than elsewhere. ③Second, fewer people lived at Cahokia than is commonly estimated (Milner estimates that there were only a few thousand inhabitants, more common estimates are 10,000 or 20,000 inhabitants); therefore, extensive taxes, trade, and tribute were not necessary to support them. ④Finally, while there is evidence of extensive earth movement, craftwork, trade, and elite at Cahokia, this does not indicate that Cahokia was politically centralized, economically specialized, or aggressively expansionistic.26.  The primary purpose of the passage is to ______