The correct answer is "A four-day religious ceremony to make pledges to the Great Spirit".
The Sun Dance is one of the most important and renowned ceremonies practiced by pretty much all Natives of the Plains region and it represented a renewal of the bond between the tribes and the earth spirit.
The ceremony started at sunrise and it involved relentless dancing while looking at the Sun for four straight days. Short breaks were allowed, but none of the participants could eat or drink in between. They would make sacrifices, specific pledges and praying for the welfare of the community.
Hope this helps!
