The Mound Builders primarily lived in the regions that encompass:
- The area from the Great Lakes to the Gulf of Mexico
- East of the Mississippi River to the Appalachian Mountains
Based on this description, you would select regions that align with those geographical boundaries, likely corresponding to Regions A and B or similar options on your map. Without seeing the actual map, I can't specify which regions are labeled A, B, etc. However, you should look for the regions that include the areas mentioned in the description.