Statement (B) is FALSE for birds. In birds, gas exchange does NOT occur in blind-ending alveoli (as in mammals) but in microscopic tubes called parabronchi, where air flows unidirectionally. This allows continuous, highly efficient gas exchange in both inhalation and exhalation. Statements (A) and (C) are true — air sacs act as bellows and two breath cycles are needed to move air through the entire system.