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 cause for contact ulcer of vocal cord \nSelect and explain. \nA. Voice abuse, B. Smoking, C. TB, D. Valignancy', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]