Oil is refined to remove naturally occurring impurities.

油经过提炼去除天然生成的杂质。

All white sugar is refined, however, this refined sugar may then be ground or coloured.

所有的白糖都是提炼过的，但是这种提炼过的白糖可能还会被碾碎或上色。

Surgical techniques are constantly being refined.

外科手术技术正在不断得到完善。

Twentieth century botanists have continually refined these classifications.

二十世纪的植物学家已经逐渐完善这些分类。