0 harmful substances in the air, often consisting of waste from vehicles or industry -- 空气污染
Diesel exhaust is a major contributor to air pollution. 柴油车辆排除的废气是空气污染的一大主因。
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。