You are answering a USMLE-style medical question. Question: A 49-year-old woman comes to the physician for a scheduled colposcopy. Two weeks ago, she had a routine Pap smear that showed atypical squamous cells. Colposcopy shows an area of white discoloration of the cervix with application of acetic acid solution. Biopsy of this area shows carcinoma-in-situ. Activation of which of the following best explains the pathogenesis of this condition? Options: A) JAK2 tyrosine kinase B) E2F transcription factors C) Phosphoprotein p53 D) Cyclin-dependent kinase inhibitors Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.