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
Transition from G2 to M phase of the ceil cycle is controlled by 
Select and explain. 
A. Retinoblastoma gene product, B. p53 protein, C. CyclinE, D. CyclinB
D: CyclinB
Answer: D: CyclinB 
Explanation: . CyclinB