Which Statement About Respiration in Birds and Mammals Is True

Which statement about respiration in birds and mammals is true?

A) Ventilation in bird lungs is bidirectional, but ventilation in mammal lungs is tidal.
B) Mammals have less dead space in their lungs than do birds.
C) Because of the efficiency of their respiratory systems, we would expect to see birds, but not mammals, at very high altitudes.
D) Air sacs are present in the respiratory systems of birds and some mammals.
E) A single breath of air remains in a mammal's respiratory system for one inhale and one exhale and in a bird's respiratory system for three cycles of inhalation and exhalation.