0 a hard substance in the outer shell of insects and animals such as shrimp and lobster, and in the cell walls of some fungi -- 壳质(某些生物体表坚硬的保护层,如昆虫、虾,龙虾的外壳和部分真菌的细胞壁)
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。