This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Pharmacology
[{'content': 'Selective Alpha 2a agonist is \nSelect and explain. \nA. Tizanidine, B. Terazosin, C. Yohimbine, D. Dexmedetomidine', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Clonidine, Tizanidine are selective alpha 2 agonists. But dexmedetomidine is more selective acting on Alpha 2a receptors-cause sedation. Used as pre-anesthetic medication. Ref: H.L. Sharma 3rd ed Pg:179', 'role': 'assistant'}]