Answer: A. To focus on how far the nation has come since its founding
Explanation:
A milestone refers to a significant event in the life of a person or thing that marks a change from their previous status. For instance, marriage is a milestone, so also is moving out of your parent's house or having your first child.
After a milestone, a new chapter begins and it is this new chapter that President Carter was referring to. The U.S. began a new chapter when they got their freedom and President Carter is trying to bring attention to this to show how far the nation had come since its founding.
