树木有助于净化空气，释放出可供我们呼吸的氧气。
Trees help keep the air clean and they make oxygen that we can breathe.
同样地，如果你收缩你的腹部，空气可以自如放出。
Likewise, if you contract your stomach, air will be automatically pushed out.
当水气凝结成水滴时，能量会被释放出来，使得周围的空气变暖。
When water vapour condenses into cloud droplets it gives up energy and warms the surrounding air.
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