But suppose you were to look at a beach from an airplane. It would seem to be all one piece of ground. It is only when you get down on that beach and look closely that you see it is really made up of small grains of sand.

• 假如你从飞机上俯瞰一个海滩，这海滩看起来就会像一整片土地，只有当你走在那海滩上并仔细观看时，你才会看到它确实是由细小的沙粒组成的。