The statement that describes the Plains Indians correctly is:
They spoke different languages but were able to communicate through sign language.
Plains Indians comprised various tribes and cultures, each with its own language but often utilized sign language for trade and communication among different groups. The other statements do not accurately reflect the history and lifestyles of the Plains Indians. While some Plains tribes practiced agriculture, many were primarily nomadic hunters relying on the buffalo. They were diverse in terms of lifestyle and beliefs, and many were not forced onto reservations until after significant westward expansion occurred.