keystone corner

例句：

1. 1. The keystone of the city's skyline is its tallest building.
   这座城市的天际线的关键石是其最高的建筑。
2. 2. The architect designed the keystone corner of the new hospital.
   建筑师设计了新医院的关键石角落。
3. 3. The construction workers were working on the keystone corner of the bridge.
   施工工人正在桥上的关键石角落工作。