Instead, birds have a complex network of air sacs that work like bellows to pump a constant stream of air through the lungs.

相反地，鸟类有一个复杂的肺泡结构，就像一个风箱把源源不断的空气打进肺里。

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The forge is blown with with a fan, but formely they used bellows and it was a hard work, if an order was urgent, a customer had to blow the forge himself.

在以前他们使用的是手风箱，工作起来非常辛苦，如果东西要得急，客人还得自己去拉风箱。

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