0 to happen or exist one after the other repeatedly -- 輪流,交替
1 with first one thing, then another thing, and then the first thing again -- 輪流的,交替的
2 a person or thing that can take the place of another -- 替代者
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。