The author groups North American Indians according to their________.

* Hướng dẫn giải

Đáp án là C. tribes and geographical regions (các bộ tộc và khu vực địa lý) . Phần đề cập đến ý này: In the Far North the ancestors of today’s Inuit hunted seals, walruses, and the great whales. They lived right on the frozen seas in shelters called igloos built of blocks of packed snow. ... The Cheyenne, Pawnee and Sioux tribes, known as the Plains fndians, lived on the grasslands between the Rocky Mountains and the Mississippi River .”