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: Surgery
Distended abdomen in intestinal obstruction is mainly due to - 
Select and explain. 
A. Diffusion of gas from blood, B. Fermentation of residual food, C. Bacterial action, D. Swallowed air
D: Swallowed air
Answer: D: Swallowed air 
Explanation: The distention of bowel proximal to the obstruction is produced by two factors