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: Surgery
[{'content': 'Secondaries in the neck with no obvious primary malignancy is most often due to - \nSelect and explain. \nA. Ca. Stomach, B. Ca. Larynx, C. Ca. Nasopharynx, D. Ca. Thyroid', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]