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. Swallowed air, C. Fermentation of residual food, D. Bacterial action
B: Swallowed air
Answer: B: Swallowed air 
Explanation: As nitrogen is not absorbed in GIT, swallowed air causes distended abdomen in intestinal obstruction.