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: Pharmacology
[{'content': "A drug 'X' is more selective for the col subtype of BZD receptors. It has hypnotic action but absent or little antianxiety, muscle relaxant and anticonvulsant actions. Which of the following can be 'X': \nSelect and explain. \nA. Zopiclone, B. Zolpidem, C. Flumazenil, D. Melatonin", 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]