Answer:
Due to exchange of gases i.e. normal and abnormal.
Step-by-step explanation:
The main difference between incomplete and complete ventilation is the occurrence of normal and abnormal exchange of gases. The mechanism in which the exchange of gas happens completely without any difficulty is called complete ventilation. It is the process in which the required amount of oxygen is inhaled or inspired and appropriate amount of carbon dioxide is exhaled out of the body while on the other hand, incomplete ventilation is a mechanism in which exchange of gases is not normal.