This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
Which of the following is not a cycling dependant kinase (CRK) inhibitor 
Select and explain. 
A. P21, B. P27, C. P53, D. P57
C: P53
Answer: C: P53 
Explanation: Ref Robbins illustrated 7/e p292, ref Robbins 8/e p286; 9/e p25_26 CyclinD form complex with cyclin dependant kinases and regulate the transition of cell cycle from one stage to other. These CDK complexes in turn are regulated by CDK inhibitor .the inhibitor controls the cell cycle by balancing the activity of CDK's .this signals from these inhibitors determine whether a cell professes through the cell cycle Changes in the level of these inhibitors may occur in some tumors or possibly in aging cells The cyclin dependant kinnase inhibitors are P21,p27,p57,p15,p16,p18p,19