建筑学中，拱道或门口的拱心石，是把建筑整体连接在一起来防止它倒塌的石头。
In architecture, a keystone in an archway or doorway is the stone that holds the whole thing together, and keeps it from collapsing.
这些有形的纽带包括驻扎在每个省的军事要塞网络和将各省与罗马连接的石造道路网络。
The physical bonds included the network of military garrisons, which were stationed in every province, and the network of stone-built roads that linked the provinces with Rome.
确保他们知道他们的诞生石手段，它是如何连接到他们。
Make sure they know what their birthstone means and how it is connected to them.
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