What is vital capacity of our lungs? 

a) 
Inspiratory reserve volume plus tidal volume 
b) 
Total lung capacity minus expiratory reserve volume 
c) 
Inspiratory reserve volume plus expiratory reserve volume 
d) 
Total lung capacity minus residual volume 
What is vital capacity of our lungs? 

a) 
Inspiratory reserve volume plus tidal volume 
b) 
Total lung capacity minus expiratory reserve volume 
c) 
Inspiratory reserve volume plus expiratory reserve volume 
d) 
Total lung capacity minus residual volume 
(d)
Total lung capacity is the sum of vital capacity and residual volume. Vital capacity of our lungs is total lung capacity minus residual volume.