This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory Failure, Subject name: Medicine
[{'content': 'Hypopnea is defined as? \nSelect and explain. \nA. > 10% reduction in airflow for at least 10 seconds with > 1% desaturation on arousal, B. > 20% reduction in airflow for at least 10 seconds with > 2% desaturation on arousal, C. > 30% reduction in airflow for at least 10 seconds with > 3% desaturation on arousal, D. > 40% reduction in airflow for at least 10 seconds with > 4% desaturation on arousal', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Hypopnea is defined as > 30% reduction in airflow for at least 10 seconds with > 3% desaturation on arousal.', 'role': 'assistant'}]