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
Beta blocker with d isomer responsible for beta blocker action is ? 
Select and explain. 
A. Nebivolol, B. Timolol, C. Esmolol, D. Propranolol
A: Nebivolol
Answer: A: Nebivolol 
Explanation: Ans. is 'a' i.e., Nebivolol Nebivolol is a novel betal-blocker with a greater degree of selectivity for betal-adrenergic receptors than other agents in this class and a nitric oxide (NO)-potentiating, vasodilatory effect that is unique among beta-blockers currently available to clinicians. Nebivolol is a racemic mixture with beta-blocker activity residing in the d-isomer; in contrast, I-nebivolol is far more potent in facilitating NO release. Note : Beta blockers with 1 isomer having beta blocking activity are :? Propranolol, atenolol, metoprolol, esmolol, timolol