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。
The keystone in the crown of an arch.
给…盖拱顶给…建造或盖以拱顶；
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