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 the following is not anti-apoptotic gene? 
Select and explain. 
A. BCL-XL, B. MCL-1, C. BCL-XS, D. BCL-2
C: BCL-XS
Answer: C: BCL-XS 
Explanation: BCL-XS is pro-apoptotic gene.