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
Which drug used in bronchial asthma needs monitoring- 
Select and explain. 
A. Theophylline, B. Cromoglycate, C. Salmeterol, D. Terbutaline
A: Theophylline
Answer: A: Theophylline 
Explanation: Ans. is 'a' i.e., Theophylline o Theophylline has low safety margin and therefore requires therepeutic drug monitoring.