flat circular stone

例句：

1. 1. The floor is very flat and smooth.
   地板非常平坦光滑。
2. 2. The table is too flat for my liking.
   这张桌子对我来说太平了。
3. 3. The car's tires are flat on the road.
   汽车的轮胎在路上爆胎了。