例句:如果我们观察水波的横截面,我们会看到波形是按一定的间隔重复的。 If we look at a cross section of a water wave, we may see that the wave form repeats itself at regular intervals.节疤这种突出物的横截面,呈圆形,比周围的地方要黑,常常出现在切割好的木材上 The round, often darker cross section of such a lump as it appea