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': 'Natural killer cell is: \nSelect and explain. \nA. MHC restricted, B. Antibody dependent, C. Null cells, D. B-lymphocytes', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. c. Null cells', 'role': 'assistant'}]