rail of self-hardening steel

例句：

1. 1. The train's wheels are set on the rails.
   火车的轮子放在轨道上。
2. 2. The workers had to remove the old rails and install new ones.
   工人们不得不拆除旧的轨道并安装新的。
3. 3. The train was traveling along the rails when it suddenly stopped.
   火车沿着轨道行驶时突然停了下来。