Answers

2015-06-10T18:24:52+08:00
Is it the bottled balloon? well, as i pull down the balloon, air goes into the small balloons represented as the lungs. 
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2015-06-13T13:53:14+08:00
When you pull down the Big Ballon (DIAPHGRAM) at the bottom of the model it contract, Causing the small Balloons (LUNGS) to Expaned/ to be fill in with air. :)
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The balloon expand because it is the process of our inhalation. As you pull down that balloon, the pressure of air in our body decreases.
Thanks you for the answers :D