___________ is the medical field which studies blood serum and other bodily fluids.

Serology is the medical field that focuses on the study of blood serum and other bodily fluids. This area of study is crucial for understanding immune responses to infections and diseases, as it involves the analysis of antibodies and antigens present in the serum. Serological tests are commonly used to diagnose various conditions, including infectious diseases, autoimmune disorders, and blood typing.

In contrast, oncology deals with the study and treatment of cancer; pulmonology specializes in the respiratory system and lung diseases; while hepatology focuses on liver conditions and diseases. Each of these fields has distinct areas of concentration that do not encompass the study of blood serum and bodily fluids in the way that serology does. Thus, serology is the correct choice for this question.