0 Something, for example a cell membrane, that is semipermeable allows some liquids and gases to pass through it, but not others. -- (細胞膜等)半透性的,半可透性的
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。