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: Medicine
[{'content': 'An asymptomatic boy on ECG is detected to have a short P interval and delta waves. The least effective measure for the boy would be - \nSelect and explain. \nA. Holter monitoring, B. Treadmill stress test, C. Beta blockers, D. Reassurance', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]