What aspect of the Columbian Exchange changed the lives of American Indians the most?

One of the first European exports to the Americas, the horse, changed the lives of many Native American tribes. The mountain tribes shifted to a nomadic lifestyle, based on hunting bison on horseback. They largely gave up settled agriculture. Horse culture was adopted gradually by Great Plains Indians.

Explanation:

could you show the options for the answers? : )

answer; ewing's sarcoma;