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 was previously used to diagnose bronchial asthma \nSelect and explain. \nA. Oxtremorine, B. Methacoline, C. Carbachol, D. Oxybutynin', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Methacholine normally acts on M2 receptor present on heart. "Methacholine challenge test" was used to diagnose bronchial asthma, where it can cause bronchoconstriction because of increased sensitivity of M3\xa0receptors due to airway hyperreactivity.', 'role': 'assistant'}]