0 in plants with flowers, a hard layer that covers and protects the surface of a seed -- 外种皮(覆盖和保护种子表面的硬皮)
We can complete it step by step however long the road is and it can't be completed however short the road is if you don't even mark your footprint.
再长的路,一步步也能走完,再短的路,不迈开双脚也无法到达。