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': 'Innate immunity active against viral cells - \nSelect and explain. \nA. NK cells, B. Cytotoxic T cells, C. B cell, D. Memory B cell', 'role': 'user'}, {'content': 'Answer: A \nExplanation: NK cells are part of innate immunity\nNK cells are considered to be important in immune surveillance and natural defense against virus-infected and malignant mutant cells.', 'role': 'assistant'}]