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: Microbiology
[{'content': 'Graft versus host reaction is caused by \nSelect and explain. \nA. B-Lymphocytes, B. T-lymphocytes, C. Monocytes, D. Leukocytes', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]