hard grinding stone

例句：

1. 1. The hard grinding stone is essential for grinding the metal.
   硬磨石对于磨金属至关重要。
2. 2. The engineer used a hard grinding stone to smooth the surface of the machine.
   工程师使用硬磨石来平滑机器的表面。
3. 3. The hard grinding stone was used in the factory to polish the machinery.
   硬磨石被用于工厂中，用来抛光机械设备。