B. a frontier region extending through several colonies, from Pennsylvania to Georgia.
Explanation:
The "backcountry" is a historical region of the United States. During the early years of the nation, the backcountry corresponded with the land behind the Appalachian border. This was considered the edge of the British colonies in the 1600s and 1700s. The backcountry was seen as remote, underdeveloped land, mostly inhabited by Native American groups.
