0 the key that you press on a computer keyboard to move the cursor (= symbol showing your place on the screen) to an earlier point -- 退格键(计算机键盘上的按键,用于将屏幕显示的光标位置后移)
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。