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: Theophylline