Due to its system of nine 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. birds generate a lot of heat, especially during flight. yet the adipose tissue under their skin and the feathers atop their skin make it difficult to eliminate excess heat across the skin. which of the following alternatives can absorb body heat and eliminate it from the bird most effectively?