Based on the description provided, the Mound Builders primarily lived in the regions that are located between the Great Lakes and the Gulf of Mexico, as well as east of the Mississippi River to the Appalachian Mountains. Therefore, the correct responses would be:
- Region A (if it is located in the area between the Great Lakes and the Gulf of Mexico)
- Region B (if it is located east of the Mississippi River, potentially reaching towards the Appalachian Mountains)
Please confirm the specific locations of the regions on the map to select the correct ones based on the descriptions.