<prompt> Closing capacity of lung is related toSmall sized bronchioles without cailage in nondependent poion of lungSmall sized bronchioles without cailage in dependant poion of lungMedium sized bronchioles without cailage in nondependent poion of lungMedium sized bronchioles without cailage in dependent poion of lung  <response>: The closing capacity CC is the volume in the lungs at which its smallest airways, the respiratory bronchioles, collapse. It is defined mathematically as the sum of the closing volume and the residual volume. The alveoli lack suppoing cailage and so depend on other factors to keep them open Ref: guyton and hall textbook of medical physiology 12 edition page number:324,325,326 