surface of equal density

例句：

1. 1.The surface of the water is still and calm.
   水面的表面仍然平静。
2. 2. The surface of the lake is covered in ice.
   湖面覆盖着冰。
3. 3. The surface of the ocean is vast and unforgiving.
   海洋的表面广阔而无情。