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
Mechanism of action of theophylline - 
Select and explain. 
A. Mast cell stabilization, B. Phosphodiesterase inhibition, C. Leukotriene antagonist, D. b2-sympathomimetic
B: Phosphodiesterase inhibition
Answer: B: Phosphodiesterase inhibition 
Explanation: Ans. is 'b' i.e., Phosphodiesterase inhibition