Air

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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 down or sleep. We 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.