You can't see it. You can't touch it. But you can't live without it. What is it? It is air.
Air is very important. It is all around us when we walk and play. It is all around us when we sit flown or sleep. Ve live in air.
All living things need air. We can live without food or water for a few days, but we cannot live without air for even a few minutes.When we are working or running,we need more air.When we are asleep, we need less air.
注释:
1) You can't live without it.没有它你就不能生存.
2) We live in air.我们生活在空气中。
3) All living things need air.一切有生命的东西都需要空气。
4) We cannot live without air for even a few minutes.没有空气，即便是几分钟我们也活不了。