That means keeping the land, water and air clean.

这意味着要保持土地、水和空气的清洁。

youdao

They keep our air clean, reduce noise pollution, improve water quality and provide food and building materials.

他们保持我们的空气清洁，减少噪音污染，改善水质，提供食品和建筑材料。

youdao

Trees reduce dust and help keep the air clean.

树木减少灰尘，有助于保持空气清洁。

youdao

The air is clean. The trees are dark and very large.

VOA: special.2009.11.16

The air is crisp and clean, unlike this room.

不像这屋子里，外面的空气新鲜又清静。

I want to 实战 - SpeakingMax英语口语达人

Today,the filters clean the air in planes.

VOA: special.2009.07.14

As Assistant EPA Administrator, Gina has focused on practical, cost-effective ways to keep our air clean and our economy growing.

WHITEHOUSE: Remarks by the President in Personnel Announcements

But setting that aside, a 30-to-1 benefit ratio to keep our air clean sounds like a mighty wise investment to me.

FORBES: A Call to Arms on Climate Change

The climate is temperate, the air clean and the sea bounteous.

CNN: WHERE IT'S GOOD TO BE OLD