<prompt> Pressure - volume curves in the lung is given here. The pressure-volume curves of the total respiratory system PTR, lungs PL, and chest wall Pw are plotted together with standard lung volumes. Point A indicate which of the following?Closing volume of lungResting lung volumeResidual volume of lungExpiratory reserve volume  <response>: Ans. B. Resting lung volumeThe pressure is zero at a lung volume that corresponds to the volume of gas in the lungs at FRC is also known as Resting Respiratory volumecapacity because the opposing forces like the elastic recoil of the lungs and the chest wall are equal and they balance each other at FRC. 