This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Increased airway resistance is/are caused by 
Select and explain. 
A. Forced expiration, B. Dense air, C. Low lung volume, D. All
D: All
Answer: D: All 
Explanation: A, B, C i.e. Forced expiration, Dense air, Low lung volume