This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Physiology
[{'content': 'Frequency of Beta waves \nSelect and explain. \nA. 5-10 Hz, B. 10-15 Hz, C. 13-30 Hz, D. None', 'role': 'user'}, {'content': "Answer: C \nExplanation: When attention is focused on something, the alpha rhythm is replaced by an irregular 13-30 Hz low-voltage activity, the beta rhythm(Ref: Ganong's Review of Medical Physiology, Twenty-Third Edition)", 'role': 'assistant'}]