This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardio thoracic surgery  , Subject name: Surgery
[{'content': 'The commonest anterior mediastinal tumour is \nSelect and explain. \nA. Aneurysm of descending aoa, B. Neurogenic tumour, C. Thymoma, D. Bronchogenic cyst', 'role': 'user'}, {'content': "Answer: C \nExplanation: Thymomas are the most common anterosuperior mediastinal tumors accounting for 25% of the total.They are commonly associated with myasthenia gravis.Diagnosis and treatment is best achieved by complete thymectomy. Reference:SRB's manual of surgery,5th edition,page no:1127.", 'role': 'assistant'}]