prepared chalk

• 研细白垩,沉降白垩,精制粉笔

prepared chalk的用法和样例：

例句

1. The teacher's chalk grated on the blackboard.
   老师的粉笔在黑板上发出刺耳的摩擦声。
2. He crushed a piece of chalk to powder.
   他将一支粉笔压成粉末。