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: Pathology
[{'content': 'Transition from G2 to M phase of the cell cycle is controlled by: \nSelect and explain. \nA. Retinoblastoma gene product, B. p53 protein, C. Cyclin E, D. Cyclin B', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]