This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Sympathetic System, Subject name: Pharmacology
Nonselective reversible a receptor blocker among the following is 
Select and explain. 
A. Phenoxybenzamine, B. Phentolamine, C. Prazosin, D. Terazosin
B: Phentolamine
Answer: B: Phentolamine 
Explanation: Nonselective irreversible a receptor blocker Phenoxybenzamine Nonselective reversible a receptor blocker Phentolamine Selective a receptor blocker Prazosin Terazosin Doxazosin