The correct answer to this open question is the following.
Although there are no options attached we can say the following.
The Appalachian Mountains have been important to the US development because this mountain chain has represented an important geographic feature in the East side of the United States. It is a natural barrier in which US history has many stories to tell.
For instance, during colonial times, many Native American tribes lived around that geographical area that represented a big obstacle to overcome to the British Troops during the French and Indian War.
The Appalachian Mountains are a large chain of mountains located on the eastern side of the United States and Canada. The Appalachian Trail is one of the most famous attractions of the region. It starts or ends in Mount Katahdin, Main, and ends in Springer Mountain, Georgia. 2,175miles for hikers.