What is the definition of a mucous membrane?

The correct answer describes a mucous membrane as the lining of various body cavities, including the nose, ears, and mouth. Mucous membranes are specialized tissues that secrete mucus, which helps to lubricate and protect these cavities. They play a crucial role in maintaining moisture, trapping pathogens, and facilitating the movement of substances in areas like the respiratory and digestive tracts.

In contrast, the other options refer to different anatomical structures or functions. A protective layer covering the skin and hair pertains to the epidermis or other forms of protective tissues, rather than a mucous membrane. Muscle tissue related to the digestive system refers to smooth muscle, which helps in peristalsis and food movement but is unrelated to the definition of a mucous membrane. Lastly, the mention of a structure that assists in bone movement refers to joints and muscles, which do not describe mucous membranes. Thus, defining a mucous membrane as the lining of various body cavities accurately captures its essential role and composition in the body.