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
Which of the following was previously used to diagnose bronchial asthma 
Select and explain. 
A. Oxtremorine, B. Methacoline, C. Carbachol, D. Oxybutynin
B: Methacoline
Answer: B: Methacoline 
Explanation: 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 receptors due to airway hyperreactivity.