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: Pediatrics
Which of the following is a feature of Acute severe asthma 
Select and explain. 
A. Heart rate of 110 beats / min, B. Pa O2 of 70 mmHg, C. Peak expiratory flow rate of < 40 %, D. All of the above
C: Peak expiratory flow rate of < 40 %
Answer: C: Peak expiratory flow rate of < 40 % 
Explanation: Features of Acute Severe Asthma

Heart rate > 120 beats / min
Pa O2 of < 60 mmHg
Peak expiratory flow rate of < 40 %