This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology and Rheumatology, Subject name: Medicine
[{'content': 'Which of the following are large, granular lymphoid cells that are mediators of antibody- dependent cellular cytotoxicity? \nSelect and explain. \nA. macrophages, B. natural killer (NK) cells, C. T lymphocytes, suppressor subset, D. B lymphocytes', 'role': 'user'}, {'content': 'Answer: B \nExplanation: NK cells may be of T-cell lineage or monocyte-macrophage lineage. They appear to play an important role in surveillance mechanisms.', 'role': 'assistant'}]