1. Light, clear gases floated upwards to mould the heaven, while weightier, impure gases sank and condensed to make the earth.
清轻之气上升，形成了天空；重浊之气下沉，凝结成大地。
2. To make impure by adding extraneous, improper, or inferior ingredients. The difficulty stems from the fact that while an externality may be seen as a cost to one group.
掺杂加入外来的，不当的或低等的成分使变得不纯困难常常来自这样的事实，即一种外在因素对一部分人可视为成本。