translation.en: If we think about the scale of size, start with an everyday object like the tennis ball, and just go down orders of magnitude in size -- from the eye of a needle down to a cell, down to a bacterium, down to an enzyme -- you eventually reach the nano-world.
translation.zh: 要想知道这个结构的大小， 那么我们从网球这种日常物品开始吧， 然后将物体按大小将序排列—— 从针眼，到细胞，到细菌，再到酶—— 最后才到纳米世界。