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': 'Mechanism of action of theophylline - \nSelect and explain. \nA. Mast cell stabilization, B. Phosphodiesterase inhibition, C. Leukotriene antagonist, D. b2-sympathomimetic', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Phosphodiesterase inhibition", 'role': 'assistant'}]