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 drug is not used in the treatment of bronchial asthma : \nSelect and explain. \nA. β2 agonists, B. Corticosteroids, C. Cholinesterase inhibitors, D. Phosphodiesterase inhibitors', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]