The correct answer is option 1, pleura. The pleura is a membrane that covers the lungs and lines the inside of the chest cavity. It helps to protect and lubricate the lungs, allowing them to expand and contract during breathing. Option 2, pericardium, is incorrect because the pericardium is the membrane that surrounds the heart. Option 3, peritoneum, is incorrect because the peritoneum is the membrane that lines the abdominal cavity. Option 4, mesothelium, is incorrect because mesothelium refers to a type of tissue that lines various organs and cavities in the body, including the pleura.