Final answer:
The small intestine is the main organ of digestion, the kidneys filter blood and generate urine, and the immune system produces antibodies, which are stored in the lymph nodes.
Step-by-step explanation:
The small intestine is the major organ of digestion in the digestive system, where further digestion and absorption take place after food has passed through the stomach. The kidneys remove waste from the bloodstream to be excreted as urine. They are involved in maintaining the dissolved ion concentrations of body fluids and are made up internally of three distinct regions - the cortex, medulla, and pelvis. Within the immune system, antibodies are produced, which are housed in the lymph nodes and play a crucial role in defending the body against pathogens. Thus, the correct answer to the question is A) Stomach; Kidneys; Antibodies.