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': 'The commonest cause of metabolic alkalosis is - \nSelect and explain. \nA. Cancer stomach, B. Pyloric stenosis, C. Small-bowel obstruction, D. Diuretics', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]