The mississippian native american group was known for building towns with what

The line dividing regions 4 & 5 on this map is known as the "fall line." which of these represents an important factor of the fall line in georgia history? a) it was the first boundary of the georgia after it became a state. b) it was an important source of power due to a change in elevation. c) it was once home to major cities that have since become abandoned. d) it was a dividing line between the united states and native american territories.