bison became the focus of another group of survivors. 野牛成为另一群幸存者的重点目标
and quickly became home to an incredible wealth of animal life. 很快成为大批动物的家园
the tundra-steppe became Earth's most extensive habitat. 冻原成为地球上最广阔的栖息地
it became a harsher, more difficult place to live. 它成为了 一个更恶劣、更难以生存的地方