The rural workforce has been flowing in to the cities ever since the open door policy was adopted.
自从改革开放政策实施以来,农付劳动力正不断流向城市。
and so the tools of long ago have remained when even the bones of the men who made them have disappeared without trace.
因此,尽管制造这些工具的人的骨头早已荡然无存,但远古时代的石头工具却保存了下来。