keystone ring

例句：

1. 1. The keystone of the mountain is a massive rock that holds up the entire structure.
   这座山的关键点是一座巨大的岩石，支撑着整个结构。
2. 2.The keystone ring was made from the same material as the other rings in the necklace.
   这个关键石环是由项链中其他戒指相同的材料制成的。
3. 3. The keystone ring symbolizes the center of the world's political and economic systems.
   这个关键石环象征着世界政治和经济体系的中心。