Final answer:
The detail from the passage that helps to develop the idea that many Americans are unaware of the greatness of the nation's national parks is that most of these places are located in remote areas, with two outside the United States. This implies that the parks are not easily accessible to the majority of Americans.
Step-by-step explanation:
The detail from the passage that helps to develop the idea that many Americans are unaware of the greatness of the nation's national parks is option B: Most of these places are located in remote areas, with two outside the United States.
This detail implies that the national parks are not easily accessible to the majority of Americans due to their remote locations. As a result, many Americans may not be aware of the greatness and beauty of these parks.
For example, if a national park is located in a remote mountainous area with limited transportation options, it would be difficult for people living in urban areas or far away from the park to visit and experience its greatness.