This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
[{'content': 'All of the following are involved in graft vs host disease except \nSelect and explain. \nA. Kidney, B. Liver, C. Stomach, D. Skin', 'role': 'user'}, {'content': 'Answer: A \nExplanation: GVHD characteristically involves liver, gastrointestinal tract and skin. It occurs as a complication of hematopoietic stem cell transplant when immunocompetent cells and precursors recognize host tissue alloantigens and react against them.', 'role': 'assistant'}]