This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General pathology, Subject name: Pathology
[{'content': 'The following is not one of the 4 key cell cycle regulators which are dysregulated in a variety of human cancers \nSelect and explain. \nA. P16/INK4a, B. Cyclin D, C. P21, D. RB', 'role': 'user'}, {'content': 'Answer: C \nExplanation: .', 'role': 'assistant'}]