沙漠的沙子，是从哪来的？

Deserts are full of sand. 沙漠里，到处都是沙子。 Where does all this sand come from? 这么多沙子，是从哪儿来的呢？ Long ago, this land was hard rock. 很久以前，这里是大块的岩石。 Hot days and cold nights crack the rock. 白天晒夜晚冻，石头裂开了。 Wind blows the pieces again and again. 风一吹，碎石子磨了又磨。 Little by little, they become fine sand. 慢慢地，它们变成了细沙。 The desert is rock worn down by time. 沙漠，就是被时间磨碎的石头。