What river serves as part of oklahoma's southern border

The Red River serves as Oklahoma's southern border. The Red River is a major tributary of the Mississippi and Atchafalaya Rivers. 

The correct answer is a. when they started making tools that will them in cultivating lands, they could raise crops and that made them attached to one place for a longer period of time. after that, they started domesticating animals and building their own permanent settlements that resemble the ones we have today.