You are answering a USMLE-style medical question. Question: A 54-year-old male makes an appointment with his primary care physician due to chronic fatigue that has left him unable to hike or do other physically demanding activities with his friends. He has well-controlled hypertension and diabetes but has otherwise been healthy. He does not smoke but drinks socially with his friends. Physical exam reveals enlarged nodules that are not tender to palpation. A biopsy is obtained showing a characteristic change in chromosome 18. The regulation of which of the following proteins will be most abnormal in this patient? Options: A) Caspase-9 B) CD15 C) Cyclin-dependent kinase 4 D) Ras pathway transcription factors Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.