The correct answer is option 1: Lung. The pleura is a thin membrane that covers and protects the lungs. It consists of two layers - the visceral pleura, which is the inner layer that is in direct contact with the lungs, and the parietal pleura, which is the outer layer that lines the walls of the chest cavity. The pleura helps to reduce friction between the lungs and the chest cavity during breathing. Additionally, it creates a sealed space called the pleural cavity, which is filled with a small amount of pleural fluid that acts as a lubricant. This allows the lungs to move smoothly during inhalation and exhalation. Overall, the pleura is essential for the proper functioning and protection of the lungs.