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': 'Sleep spindles and K complexes occur in which phase of the sleep cycle \nSelect and explain. \nA. REM, B. Stage I, C. Stage II, D. Stage III', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Sleep spindles are sudden bursts of oscillatory brain activity generated during stage 2 of NREM sleep.K complexes are large waves that react to external stimuli while sleeping also seen during stage 2 of NREM sleep.', 'role': 'assistant'}]