hardened links

例句：

1. 1.The metal has hardened from the heat.
   金属因高温而变硬了。
2. 2. The ground hardened as it dried.
   地面在干燥后变硬了。
3. 3. The old car's engine has hardened over time.
   旧车发动机随着时间的推移变得更硬了。