A pitfall trap can be any small container placed in the ground with the top level with the surrounding surface and filled with a preservative.
陷阱可以是任何放置在地面上的小容器，其顶部与周围的表面齐平，并装满防腐剂。
The iron wheels of carriages ground the stones of the top level into a continually smoother and more watertight surface.
当时马车的铁轮不断地将那些碎石碾得越来越平整、防水性越好的磨损面。
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