air sac

例句：

1. 1. The bird's lungs are filled with air sacs that allow it to breathe.
   鸟的肺里充满了空气囊，使它能够呼吸。
2. 2. The fish swims in a watery air sac, which is like a bubble.
   鱼在水中游动，它的身体就像一个气泡。
3. 3.The scientist discovered an air sac inside the animal's body that could be used for communication.
   科学家在动物体内发现了一个气囊，可以用来进行沟通。