How Has the Avian Lung Adapted to the Metabolic Demands

Multiple Choice

How has the avian lung adapted to the metabolic demands of flight?

A) Airflow through the avian lung is bidirectional like in mammals.
B) There is more dead space within the avian lung so that oxygen can be stored for future use.
C) Countercurrent circulation is present in the avian lung.
D) Gas exchange occurs during both inhalation and exhalation.