What do body cavities primarily host?

Body cavities primarily serve as spaces within the body that house internal organs, providing them with a protective environment and allowing for movement and function. For instance, the thoracic cavity contains the heart and lungs, while the abdominal cavity holds organs such as the stomach, liver, and intestines. These cavities are essential for the organization of the body's structures and support the functionality of the organs housed within them.

The other options do not accurately reflect the primary function of body cavities. While blood vessels run through these cavities, they are not the main occupants. Nerves and neurons are found throughout the body but are not contained within cavities specifically. Similarly, muscles and connective tissues support and surround organs but are not primarily what the cavities host. Hence, the focus on internal organs distinctly highlights the role of body cavities.