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
[{'content': 'Which of the following is beta-blocker antagonist \nSelect and explain. \nA. Glucagon, B. Neostigmine, C. Ambenonium, D. All of the above', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., GlucagonGlucagon is used in beta-blocker poisoning to combat bradycardia produced by b-blockers. Glucagon acts by increasing C-GMP in myocardium, in effect bypassing p-receptors )Action is independent of beta receptors.", 'role': 'assistant'}]