Final answer:
Serous fluid is found in the peritoneal, pleural, and pericardial cavities, but not in the spinal cavity as it contains cerebrospinal fluid and is not lined by serous membrane.
Step-by-step explanation:
Serous fluid can be obtained from the peritoneal, pleural, and pericardial cavities but not from the spinal cavity. This is because serous membranes line body cavities that are closed to the exterior, specifically the peritoneal cavity surrounding abdominal organs, the pleural cavity surrounding the lungs, and the pericardial cavity surrounding the heart. The spinal cavity, however, is filled with cerebrospinal fluid and is part of the central nervous system, which is not lined by serous membrane.