flat folded seam

例句：

1. 1. The floor is made of a smooth, flat material.
   地板是由一种光滑、平整的材料制成的。
2. 2. The table is flat and easy to clean.
   桌子是平的，容易清洁。
3. 3. The car has a flat tire.
   汽车轮胎爆胎了。