The following graph shows a relation between lung volume and intrapleural pressure changes during inspiration & expiration. What is the most likely cause

"The pressure volume curve of the lung is not the same in inspiration and exhalation. This difference is called hysteresis, and it is caused by the action of surfactant" The compliance is higher during expiration than during inspiration The difference between the inflation and the deflation paths-hysteresis- exists because a greater transpulmonary pressure is required to open a previously closed airway The alveolar environment, and specifically the secreted factors that help reduce surface tension and keep alveoli from collapsing, contribute to hysteresis.