Answer:
The correct answer is option 4.
Step-by-step explanation:
According to the given excerpt, it is stated that the Yellowstone has been home to the Native Americans for quite a number of years.
In 1872 however, even though the United States was yet to reach 100 years old named the Yellowstone park as the first national park in the world.
Therefore, the reference to the United States centennial helps the reader understand that the US government provided a national park even though they were not up to 100 years of age.