This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Pharmacology
Drugs which increase level of Theophylline include 
Select and explain. 
A. Ciprofloxacin, B. Cimetidine, C. Allopurinol, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Refer KDT 6/e p 221 Drugs which inhibit Theophylline metabolism and increase it's plasma level are Erythromycin Ciprofloxacin Cimetidine OCP Allopurinol