The correct answer is A) defined border.
In the reservation system, American Indians tribes were confined to assigned land with a defined border.
The United States government created the Reservation System to keep the Indians off the lands white people wanted to settle. The Native American Indians tribes have lived in their territories for thousands of years but eth US government decided to use those lands to settle new white people. So Native American Indians were sent to Reservations where they could maintain their culture and traditions until the Daws Act of 1867eliminated this system of Indian Reservations in that it divided them into individual portions of land.