硬如铁的

例句：

1. 1. The iron ore is mined from the mountains.
   铁矿石从山上开采。
2. 2. He used a hammer to hit the nail into the wall.
   他用锤子把钉子敲进墙上。
3. 3. The iron gates were rusted and in need of repair.
   铁大门生锈了，需要修理。