finest grade of graphite

例句：

1. 1.The finest grade of graphite is usedin the production of high-quality pencils.
   最优质的石墨用于生产高质量的铅笔。
2. 2.The engineer used the finest grade of graphite to make the machine more efficient.
   工程师使用最优质的石墨使机器更加高效。
3. 3.The finest grade of graphite was usedto coat the surface of the metal toimprove its strength and durability.
   最优质的石墨被用来涂覆金属的表面，以增强其强度和耐用性。