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
Therapeutic blood range of theophylline in microgram per L is: 
Select and explain. 
A. 0-5, B. 10-May, C. 15-May, D. 20-May
D: 20-May
Answer: D: 20-May 
Explanation: Theophylline is having a narrow margin of safety so therapeutic drug monitoring is essential If levels increase more than 20mg/L- side effects occurs ESSENTIAL OF MEDICAL PHARMACOLOGY SEVENTH EDITION KD TRIPATHI PGNO.226