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
All the following decrease skeletal muscle tone by CNS effects except: 
Select and explain. 
A. D-tubocurarin, B. Diazepam, C. Beclofen, D. Mephensin
A: D-tubocurarin
Answer: A: D-tubocurarin 
Explanation: None