Due to its system of air sacs connected to the lungs, the respiratory system of birds is arguably the most effective respiratory system of all air-breathers. Upon inhalation, air first flows into posterior air sacs, then into the lungs, and then into anterior air sacs on the way to being exhaled. Thus, there is one-way flow of air through the lungs, along thousands of tubules called parabronchi. The one-way flow of air along parabronchi makes what type of gas exchange mechanism possible, at least theoretically? A) the same as that occurring in fish gills
B) the same as that occurring in insect tracheae
C) the same as that occurring in mammalian lungs
D) the same as that occurring in echinoderm skin gills