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
[{'content': 'Distended abdomen in intestinal obstruction is mainly due to - \nSelect and explain. \nA. Diffusion of gas from blood, B. Fermentation of residual food, C. Bacterial action, D. Swallowed air', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The distention of bowel proximal to the obstruction is produced by two factors', 'role': 'assistant'}]