flatness of wave

例句：

1. 1. The flooris very flat and easy to clean.
   地板非常平坦，容易清洁。
2. 2. Thecar's suspension systemneeds to be checked for flatness.
   汽车的悬挂系统需要检查是否平整。
3. 3. The surface of the lake isvery flatness, perfect for swimming.
   湖面非常平坦，非常适合游泳。