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. Swallowed air, C. Fermentation of residual food, D. Bacterial action', 'role': 'user'}, {'content': 'Answer: B \nExplanation: As nitrogen is not absorbed in GIT, swallowed air causes distended abdomen in intestinal obstruction.', 'role': 'assistant'}]