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
Relatively higher dose of theophylline is required to attain therapeutic plasma concentration in : 
Select and explain. 
A. Smokers, B. Congestive heart failure patients, C. Those receiving erythromycin, D. Those receiving cimetidine
A: Smokers
Answer: A: Smokers 
Explanation: None