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: Medicine
Residual volume is best measured by ? 
Select and explain. 
A. Body plethysmography, B. Helium dilution method, C. Spirometry, D. All of above
A: Body plethysmography
Answer: A: Body plethysmography 
Explanation: Answer- A. Body plethysmographypulmonary plekysmographs are commonly used to measure the functional residual capacity (FRC) of the lungs - the volumein the lungs when the muscles of respiration are relaxed - and total long capacity