Which type of membranes line the organs within the thorax, abdominal, and pelvic cavities?

Serous membranes are the correct answer because they specifically line the thoracic, abdominal, and pelvic cavities, providing the necessary lubrication for organ movement within these body cavities. These membranes create a smooth, fluid-filled environment that reduces friction between the organs and the walls of the cavities, facilitating movement during processes such as respiration and digestion.

In contrast, mucous membranes line cavities that open to the exterior, such as the respiratory and digestive tracts, which is not applicable to the organs within the thoracic, abdominal, and pelvic cavities. Synovial membranes are located in joint cavities and help to reduce friction between bone surfaces during movement, while cutaneous membranes refer to the skin, which is the outer protective layer of the body. Therefore, serous membranes, with their role and specific location in the body, are the most appropriate choice for lining the organs in the mentioned cavities.