Answer: C. The pleural cavity
Explanation: The pleural cavity is a small space between two tissues found in the lung. This cavity is filled with a small amount of fluid known as pleural fluid. The purpose of pleural fluid is to keep the lung tissue smooth and lubricated as the lung expands and contracts while breathing. Thus, the presence of pleural fluid makes lung movements easier while breathing. However, too much pleural fluid can put pressure on the lungs and cause difficult breathing.
The abdominal cavity is a large space in your abdomen that contains much of you digestive organs such as the intestines and liver. It does not contain any respiratory organs, so choice A is incorrect. There is serous fluid that lubricates the abdominal organs, but it doesn't aid in respiration.
The pericardial cavity refers to a space found between the tissues of the heart. It is also filled with fluid to lubricate the organ, but since the heart is a circulatory organ and not a respiratory organ, choice B is also incorrect.
The pelvic cavity is a space found within the middle of the coxa bones. This cavity contains many of our reproductive and urinary organs, such as the bladder, testes, and ovaries. It does not contain any respiratory organs, so choice D is also incorrect.