Birds have a system of _____ and _____ that serve to exchange gases.
a. spiracles; lungs
b. air sacs; spiracles
c. air sacs; lungs
d. gills; lungs
e. gills; spiracles
The bird's respiratory system consists of paired lungs, which contain static structures with surfaces for gas exchange, and connected air sacs, which expand and contract causing air to move through the static lungs
