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
While advancing there is increased chance of developing cancers. Tumorigenesis in aging is due to: 
Select and explain. 
A. Telomerase reactivation, B. Telomerase inactivation, C. Increased apoptosis, D. Suppression of proto-oncogenes
A: Telomerase reactivation
Answer: A: Telomerase reactivation 
Explanation: Telomerase is a ribonucleoprotein that is expressed in stem cells and most cancer cells, but not in somatic cells. More than 90% of human cancers express high levels of telomerase that prevent telomere shoening to critical levels and allow indefinite cell proliferation. Ref: Longo D.L. (2012). Chapter 84. Cancer Cell Biology and Angiogenesis. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.