Final answer:
The correct statements about expiration are A) Alveolar pressure increases and C) Expiration is typically a passive process. The abdominal muscles do not contract during normal expiration, and the diaphragm contracts during inspiration, not expiration.
Step-by-step explanation:
The correct statements about expiration are: A) Alveolar pressure increases during expiration and C) Normally expiration is a passive process.
During expiration, the diaphragm relaxes and moves upward, which leads to a decrease in the thoracic cavity volume and an increase in intra-alveolar pressure. This increase in pressure forces air out of the lungs. Expiration is usually a passive process driven by the lung's elasticity, rather than active muscle contraction. However, in forced expiration, such as during vigorous exercise or coughing, the abdominal muscles contract to expel air more forcefully.
The statement B) The abdominal muscles contract during normal expiration is incorrect because the abdominal muscles typically do not contract during normal, passive expiration; they become involved only during forced expiration. The statement D) The diaphragm contracts during expiration is also incorrect as the diaphragm actually relaxes during expiration after having contracted during inspiration.