0 a way of walking with one person behind another -- 单行,一路纵队
The schoolchildren were told to walk in single file. 小学生们被要求排成一路纵队前进。
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。