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: Physiology
[{'content': 'Without external cue, the sleep-wake cycle in humans \nSelect and explain. \nA. Unchanged, B. Continues with cycle length of > 24 hours, C. Continues with cycle length of < 24 hours, D. Continue with cycle length of > 12 hours', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Normal sleep-wake cycle in humans- 24 hrs\nWhen external cues (Light and darkness) removed, sleep-wake cycle- Slightly increased (>24hrs)', 'role': 'assistant'}]