题目解析:
原文高亮句主干为 the hunter-foragers’ overall impact on their environment was low;
由 since 带出原因,考查因果逻辑,原因(1)these bands were small in size,原因(2)never stayed in one place for a sufficient period of time,直接结果是没有带来 long-term effect on the plant and animal populations,进而的核心结果为 the hunter-foragers’ overall impact on their environment was low。
故选 C。