planar cross set

例句：

1. 1. The floor is planar and smooth.
   地板是平面且光滑。
2. 2. Thetable is planar andstable.
   桌子是平面且稳定。
3. 3. The roof of the house is planar and can be easily repaired.
   房子的屋顶是平面的，可以很容易地修理。