Which of the following structures encloses the lungs?

The structure that encloses the lungs is the pleura. The pleura is a double-layered membrane consisting of the visceral pleura, which directly covers the lungs, and the parietal pleura, which lines the chest cavity. This configuration not only serves to protect the lungs but also provides a frictionless surface that allows for smooth movement during respiration. The pleural cavity, the space between these two layers, contains pleural fluid, which further aids in reducing friction and allows the lungs to expand and contract efficiently during breathing.

In contrast, the other options do not accurately represent any anatomical structure that surrounds or encloses the lungs. The pseudo-sternum is not a recognized anatomical term associated with lung anatomy. The pneumonic envelope is not a standard term used in respiratory anatomy. Pleurisy refers to inflammation of the pleura, which can cause pain and other symptoms but does not describe a structural component. Thus, the pleura is definitively the correct answer among the choices provided.