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
[{'content': 'In exocrine pancreatic cancer, the commonest tumour marker to be elevated as - \nSelect and explain. \nA. CA-125, B. CEA, C. CA-15-3, D. CA-19-9', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]