flat Pratt truss

例句：

1. 1. The floor is very flat andeasy to clean.
   地板非常平坦，容易清洁。
2. 2. The car was parked on aflat surface.
   汽车停在一个平坦的表面。
3. 3. Theroof of the house is flat and doesn't slope.
   房子的屋顶是平的，没有倾斜。