What covers the lungs as a thin layer of tissue?

The visceral pleura is a crucial structure in the respiratory system, specifically relating to the lungs. It is a thin layer of tissue that directly covers the lungs themselves, enveloping their surface and providing a protective layer. This membrane helps to reduce friction between the lungs and the chest wall during the process of breathing, allowing for smoother expansion and contraction of the lung tissue.

In contrast, the parietal pleura is a different layer that lines the chest cavity, creating a space between it and the visceral pleura known as the pleural cavity. While serous membranes do cover other organs in the body and provide similar protective functions, the visceral pleura specifically pertains to the lungs. Adipose tissue, meanwhile, is a type of connective tissue related to fat storage and is not involved in the protective covering of the lungs. Thus, the visceral pleura's specific role in directly covering and protecting the lungs is what establishes it as the correct answer.