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
Which of the following is not an adrenergic neuron blocking drug? 
Select and explain. 
A. Reserpine, B. Guanethidine, C. Bretylium, D. Minoxidil
B: Guanethidine
Answer: B: Guanethidine 
Explanation: None