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: Unknown
All of the following can be measured by a simple spirometer except. 
Select and explain. 
A. Tidal volume, B. FEV1, C. Residual volume, D. Vital capacity
C: Residual volume
Answer: C: Residual volume 
Explanation: Ans. is 'c' i.e. Residual volume Residual volume (which is the amount of air remaining in the lungs at the end of forced expiration) cannot be measured by simple spirometer because the air in the residual volume of lungs cannot be expired into the spirometer. To measure residual volume, spirometer is used in a special way - by means of helium dilution method*.