This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Physiology
True about normal expiration 
Select and explain. 
A. At the end of normal expiration air in lung is ERV, B. Chest wall has a tendency to move outward which is balanced by inward recoil of alveoli, C. In expiration pleural pressure is equal to alveolar pressure, D. Muscles that elevate the chest cage are classified as muscles of expiration
A: At the end of normal expiration air in lung is ERV
Answer: A: At the end of normal expiration air in lung is ERV 
Explanation: Your expiratory reserve volume is the amount of extra air -- above anormal breath -- exhaled during a forceful breath out. The average ERV volume is about 1100 mL in males and 800 mL in females Ref: guyton and hall textbook of medical physiology 12 edition page number:324,325,326