after hardening

例句：

1. 1.The sun has hardened the ground beneath our feet.
   阳光已经使我们脚下的土地变得坚硬。
2. 2.The old tree had hardened over time.
   这棵老树随着时间的推移已经变得坚硬了。
3. 3. The metal was hardened by heating it in a furnace.
   金属通过在炉中加热而变硬。