This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Neoplasia, Subject name: Pathology
[{'content': 'Which is not seen in the anterior mediastinum:(1987) \nSelect and explain. \nA. Teratoma, B. Thymic tumours, C. Thyroid tumours, D. Neurofibroma', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans: d', 'role': 'assistant'}]