The correct answer to this open question is the following.
Although you forgot to include the excerpt and the options of the question, we can say the following.
Despite geographic separation and diverse environments, many American Indian peoples used some common practices. According to the excerpt, the practice that was unique to the Plains Indians was the use of domesticated horses in hunting and warfare.
These Native American Indian tribes used horses for primary necessities and activities to survive. They were farmers and hunters. They needed to go hunt animals to feed their families. In the 1600s, the horse represented the chance to effectively hunt animals and a great asset when they wage war against other tribes. Among these tribes that used to hunt Buffaloes as their primary hunt, were the Comanche, Arapaho, Cheyenne, Apaches, and Lakotas.