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: Anaesthesia
[{'content': 'The volatility of an anesthetic agent is directly proportional to lowering the flow in the portal vein. Portal flow is maximally reduced by – \nSelect and explain. \nA. Ether, B. Halothane, C. Isoflurane, D. Enflurane', 'role': 'user'}, {'content': 'Answer: B \nExplanation: All volatile anaesthetic agents reduce portal hepatic blood flow. This decrease is greatest with halothane and least with isoflurane.', 'role': 'assistant'}]