犹如弯弓的单拱，在与人行通道连接之处是非常之薄，在向地面延伸的过程中逐渐变厚。
The bowed arches of the single-span design are dramatically thin where they connect with the walkway, but they flare out as they approach the ground.
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.
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