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': 'HLA HI gene codes for - \nSelect and explain. \nA. Immunological reaction in graft rejection, B. Complement, C. Graft versus host reaction, D. Immunoglobulins', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Complement", 'role': 'assistant'}]