50公斤重的大马哈鱼王曾经奋力爬上瀑布，把卵产在砾石床上，现在只有混凝土墙挡住静止的水和深深的泥床。
Where 50-kilogram king salmon once fought their way up waterfalls to lay their eggs in gravel beds, there now are only concrete walls holding back still water and deep beds of muddy deposits.
蒸汽压路机把砾石路基压平后浇灌了混凝土。
The steam-roller levelled out the gravel roadbed and then the concrete was poured.
对于一层来说，混凝土平屋顶有砾石层防止热量进入建筑。
For the ground floor, the flat concrete roof has a layer of gravel to prevent heat from entering the building.
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