arch keystone

基本解释

To effect change means not just replacing the keystone but painstakingly rebuilding the arch.
施行改革并不只是更换一块拱心石，而是要费心费力的重新建立一个拱门。
A wooden frame built especially to support the sides of an arch until the keystone is positioned.
支拱板条专门用来在拱顶石放置好以前支撑拱的两边木架子。
Pennsylvania's nickname is the Keystone State. Just as a keystone holds together a stone arch, Pennsylvania was seen as holding together the young American republic.
宾夕法尼亚州的别名是“拱心石之州”。就如拱心石支撑起石拱一样，人们认为宾夕法尼亚支撑起了年轻的美利坚共和国。

Just as a keystone holds together a stone arch, Pennsylvania was seen as holding together the young American republic.