a:  Alveoli ~
b:  tiny bags of air
What:  
"Alveoli are like tiny bags of air with walls so thin that gases can pass through them. There are around 300 million alveoli in the lungs "
Useful?
Writer:  Not Stated
LCC: 
Where:
Date:   Mar 12 2015  7:18 PM
# 7518 Critique Analogy
