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: ENT
[{'content': 'The most common cause of unilateral left vocal cord palsy is - \nSelect and explain. \nA. Carcinoma thyroid, B. Trauma, C. Carcinoma esophagus, D. Idiopathic', 'role': 'user'}, {'content': 'Answer: B \nExplanation: This question is tricky one.\nMost common cause of left recurrent laryngeal nerve (vocal cord) paralysis is bronchial malignancy at the left hilum.\nSecond most common cause is iatrogenic (surgical) trauma.', 'role': 'assistant'}]