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': 'All the following decrease skeletal muscle tone by CNS effects except: \nSelect and explain. \nA. D-tubocurarin, B. Diazepam, C. Beclofen, D. Mephensin', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]