pollution

空气污染是许多大城市的一个严重问题。

Air ___pollution is a serious problem in many major cities.

我们都应该通过少开车来努力减少污染。

We should all try to reduce ___pollution by using our cars less.

这里的污染比城市少，而且也更安静。

There is less ___pollution than in the city and it is quieter too.