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': 'The commonest site for extragonadal germ cell tumour is - \nSelect and explain. \nA. Retroperitoneum, B. Sacrococcygeal region, C. Pineal gland, D. Mediastinum', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]