滚雪球层进式阶梯倍投简介：Because the border is far away, long-distance transportation of grain is expensive, so merchants from Shanxi and Shaanxi hire inland labor to cultivate fields at the border and produce grain on site in exchange for salt.
Because the border is far away, long-distance transportation of grain is expensive, so merchants from Shanxi and Shaanxi hire inland labor to cultivate fields at the border and produce grain on site in exchange for salt.
