grade surface的用法和樣例：
例句
- The fine grains are more at the tail than at the foreside at the same parallel to the slope surface.
沿坡面方向，在離土面相同距離的位置，後部細顆粒多，前部細顆粒少。 - The wetting front moved nearly parallel to the soil surface, and its length could be described by a power function of time, when the distribution of initial soil water was uniform.
當初始含水量分佈均勻時，降雨入滲過程中濕潤鋒面幾乎平行坡面運移，濕潤鋒深度與時間的關係可用冪函數描述。
