空气

Air is all around us. We can live without food or water for days, but not without air.

空气在我们周围。我们可以几天不吃不喝，但不能没有空气。

We cannot see air, but we can feel it when it moves. Moving air is called wind.

我们看不见空气，但空气流动时能感觉到。流动的空气叫风。