Final answer:
The type of membrane that lines open body cavities is a mucous membrane, as opposed to serous membranes which line closed body cavities.
Step-by-step explanation:
The type of membrane that lines open body cavities is known as a mucous membrane. Mucous membranes are one of the three types of epithelial membranes, which also include serous membranes and the cutaneous membrane (skin). Mucous membranes are found lining body cavities and tubes that have connections to the external environment, such as those in the respiratory, digestive, urinary, and reproductive systems. In contrast, serous membranes line body cavities that are closed to the exterior, such as the thoracic cavity (including the pericardial cavity around the heart and the pleural cavities around the lungs) and the peritoneal cavity in the abdomen.
Serous membranes are composed of a layer of simple squamous epithelium known as mesothelium supported by connective tissue. They secrete a lubricating serous fluid that helps reduce friction between the body's internal organs. Hence, in your schoolwork question, the correct answer to the type of membrane that lines an open body cavity would be B) mucous membrane.