Final answer:
The abdominal cavity provides the least protection to its internal structures.
Step-by-step explanation:
The body cavity that provides the least protection to its internal structures is the abdominal cavity. The abdominal cavity houses the digestive organs, such as the stomach and intestines, which are not as vital or fragile as the structures found in the cranial, thoracic, or pelvic cavities. For example, the cranial cavity protects the brain, which is a crucial organ that controls numerous bodily functions, while the thoracic cavity protects the heart and lungs. On the other hand, the abdominal cavity contains organs involved in digestion, which can withstand a certain degree of external pressure or impacts.