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
Hypopnea is defined as? 
Select and explain. 
A. > 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
C: > 30% reduction in airflow for at least 10 seconds with > 3% desaturation on arousal
Answer: C: > 30% reduction in airflow for at least 10 seconds with > 3% desaturation on arousal 
Explanation: Hypopnea is defined as > 30% reduction in airflow for at least 10 seconds with > 3% desaturation on arousal.