Question: Alveolar ventilation is the volume of air that: 
 Options:  <1> It enters (or exits) the lungs in each breath. <2> It enters (or exits) in the airways every minute. <3> It remains in the alveoli after a normal expiration. <4> Enter (or exit) in the lung exchange zones in one minute <5> It remains in the alveoli after a forced expiration.
4