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
[{'content': 'Relatively higher dose of theophylline is required to attain therapeutic plasma concentration in : \nSelect and explain. \nA. Smokers, B. Congestive heart failure patients, C. Those receiving erythromycin, D. Those receiving cimetidine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]