0 the mass of a specific isotope of a particular chemical element, usually expressed in atomic mass units -- 原子質量(某化學元素同位素的質量,通常以原子質量單位的形式表達)
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。