Critical Closing volume is

Ans is 'd' i.e. Close to Residual Volume [Ref: Physiologic Basis of Respiratory> Disease by Qutayba Hamid, Joanne Shannon, James Martin pi37; Surgical Critical Care and Emergency Surgery: Clinical Questions and Answers By Forrest O. Moorep7; http://www.ccmtutorials.com/rs/peep/page4.htmCritical closing volume is the minimum volume and pressure of gas necessary to prevent small airway collapse. It is somewhat near Residual volume.Under pathological conditions when CCV exceeds Functional Residual Capacity (FRC), alveolar collapse occurs.FRC is = Residual volume + Expiratory reserve volume