Many Plains Indians had trouble living on reservations because they were

nomadic hunters.

farmers.

day laborers

explorers.

The answer is;

A. Nomadic Hunters

The American nation began to expand west during the middle eighteen hundreds. People settled in the great open areas of the Dakotas, Utah, Wyoming, and California. The movement forced the nation to deal with great tribes of native American Indians. The Indians had lived in the western territories for hundreds of years