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
Which of he following is not a cyclin dependent kinase (CDK) inhibitor? 
Select and explain. 
A. p21, B. p27, C. p53, D. P57
C: p53
Answer: C: p53 
Explanation: . p53