What does the prefix "pneumo-" refer to, typically?

The prefix "pneumo-" is derived from the Greek word "pneuma," which means "breath" or "air." When this prefix is used in medical terminology, it commonly refers to aspects related to the lungs or the respiratory system. For instance, terms like "pneumonia" (inflammation of the lung) and "pneumothorax" (air in the pleural space) both utilize this prefix to indicate their relation to air or the lungs.

The other options refer to completely different systems in the body. The digestive system involves organs responsible for breaking down food, the excretory system pertains to waste removal and urine production, and the nervous system relates to the brain, spinal cord, and nerves. Thus, the correct association of "pneumo-" with air or lungs firmly supports the accuracy of the provided answer.