arch keystone

基本解释

To effect change means not just replacing the keystone but painstakingly rebuilding the arch.
施行改革竝不衹是更換一塊拱心石，而是要費心費力的重新建立一個拱門。
A wooden frame built especially to support the sides of an arch until the keystone is positioned.
支拱板條專門用來在拱頂石放置好以前支撐拱的兩邊木架子。
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.
賓夕法尼亞州的別名是“拱心石之州”。就如拱心石支撐起石拱一樣，人們認爲賓夕法尼亞支撐起了年輕的美利堅共和國。

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